evgaken1
Accidental solution found(maybe):
So after Im trying to ease the pain of plugging unplugging USB cables several times per day I bought myself an USB hub from Amazon the thing with 4 individual push on/off buttons, and installed right next to my keyboard to plug the X15 mouse in.
 
Guess what? 2 days passed and I have no issue of disconnect!  my version is 1.0.10 and  firmware  1.45  I do not know how long will it last or does it actually fix the issue.  If you have some kind of usb hub maybe worth a try.

Even if it doesn't fix it, it still saves wear and tear on your usb ports. I've started doing the same but with a simple extender I already have for my ps1 controller dongle. Granted USB ports now are made for thousands of unplugs/plugs but no need to put stress on them if you don't have to. 

Mocekga
Any news on when a fix is coming for the random disconnects? Or would it be better to stop wasting time and just use it as a target to shoot at and buy from a better company?

No real news. I put in a complaint on the evga website and got a reply of them having no knowledge of the issue. At this point I think evga just expects us to accept that we paid money for a defective product-line and hope we forget about it down the road when its time to drop $1000 on a new gpu. 

While I have an RMA open, I haven't completed it because of the issues other users have indicated with having similar troubles from RMA'd replacements so instead I just bought a different mouse. While I love the feel and button configuration on the X15, the random disconnects just kill using it for anything. I'm sure its problematic trying to track down the issue as well for the firmware developers. There doesn't seem to be any visible reason for the disconnects. I have had the mouse work for hours at a time, other times the mouse fails as my PC boots up. I've tried changing which USB port the mouse is connected to, using powered USB hubs, and made sure all my hardware firmware and drivers are up to date. I have had to resort to keeping an old mouse "on standby" for when this one fails. Then I go through a process of multiple re-connections of the X15 to get it to function again.
 
I have to wonder if the mouse isn't filtering out all the USB packets that are supposed to be sent to a different device on the bus and so the USB packet locks up the mouse causing it to fail to communicate. I have noticed that it is much harder to get the X15 to start back up when I have my other mouse plugged in, as if it only is filtering for "mouse type device" instead of it's own assigned USB id, but it still has trouble occasionally when I don't have another mouse plugged in so it is possible one of my other input devices "acts" enough like a mouse that it can cause issues.

elvinmagical
I was able to downgrade my mouse firmware with the following steps:

1. Download EVGA Unleash RGB software version 1.0.13.0:
2. Extract the EXE file to a new folder using 7-Zip
3. Open Library\X15RGBLibrary.dll with a binary-safe text editor (Notepad++)
4. Search for the string "X15_v1.28.bin", which is the last good firmware file as of now (the file itself can be found in Firmware folder)
5. Look for the number after file name ("284"), it's the firmware's internal version and compared with the one from connected mouse
6. Modify it to become 291 (the latest/buggy firmware v1.34 has internal version of 290, according to Library\X15RGBLibrary.dll found in driver version 1.0.15.0)
7. Quit any running EVGA driver, run extracted UnleashRGB.exe, it will attempt a firmware "update" (downgrade to v1.28) because mouse-reported firmware version is 290, lower than 291
8. After finishing the update, the driver will attempt to update again (this time it's 284 < 291), cancel it
9. Voila! Your X15 mouse firmware is now downgraded to v1.28.

The 1.0.13.0 driver can then be installed normally. Don't forget to disable auto-update this time.
(EVGA, please don't patch it in a future release. We need this trick to prevent other undesired firmware updates done accidentally.)

I'm having a similar problem. I may find myself coming to this guide very soon.

EVGATech_JaesonW
Product Management is aware, and should be fixed in the next update. No ETA for when that will be available unfortunately. In the mean time, if you're having issues with the latest firmware, you can download an older one here and flash it until the next update - 

 
I think I have a pretty easy solution to this issue. 
 
I managed to use the tool linked by EVGATech_JaesonW above downgrade my firmware to 1.28 (I cannot link it for some reason).
Steps:

1. Download the tool linked above and extract to your desktop. 
2. Download and install EVGA Unleash RGB software version 1.0.13.0 (  )
3. Copy "X15_v1.28.bin" (located in C:\Program Files (x86)\EVGA\Unleash RGB\Firmware)
4. Paste into the firmware tool folder you extracted to your desktop
5. Rename "X15_v1.28.bin" to "_X15_v.bin"
6. Run "_X15Update.bat"
7. Run EVGA unleashed and check settings to see if the firmware downgraded. 

 
So far, the mouse is running much better especially on bootup. 
Will report if I have any issues. 

Need EVGA serious fix on this issue ASAP, its been too long and too bad for this company to ignore such critical bugs for their products!

I haven't been having disconnects like I used to have on my keyboard and mouse, so it does seem like the firmware update helped. I did have it happen a few times while in windows before the update but oddly I can't remember it happening ever while in a game. It also it seems like one of the firmware updates fixed having to unplug and replug in the mouse and keyboard when they disconnected. Last few times I had the mouse disconnect it was just for like enough time to be annoying and then it would reconnect.

Seemed to be fixed for awhile for me but just updated to the latest firmware 3 days ago
and the disconnects are back. Seriously dumbfounded that this has not been fixed considering
how long EVGA have known about it.
Come on EVGA, this is just straight out incompetence.

I have had this same problem for months now and I think I just solved it two days ago. If you have a PC (I have an jet engine, I mean a "gaming" laptop, so I have access to a touchpad which does not seem to interfere with this process) set shortcuts on the top of your desktop so you can do this quickly with the tab key, not tapping it a thousand times. I went into the device manager and uninstalled every other mouse driver, even the HID ones. EVERYTHING in the mouse drivers. I uninstalled the Unleashed software too. Then I went to the EVGA page and downed Unleashed and opened it. Nothing shows in the software since there are no drivers. Then I plugged the X15 and it appeared instantly. I have not had a single disconnect since. The mouse would disconnect randomly and when I made a flickshot or lift the mouse itself. Now it is a normal ****ing mouse again. The only thing I cannot explain is why the **** the keyboard and mouse turn on sometimes when my laptop is off with the lid closed. I have tried freaking everything but this is not the forum for that issue. I hope this really helps anyone. GGs.

Its been too long, I already ditched this company.  I bet they are still thinking why we should care about this cheap product we mass produced in China that serve no real purpose except to annoying buyers, its not gonna hurt the company at all.  You know what? its already hurting you!
 
I have switched to other mmo mouse and got used to it already, never gonna look back on this most annoying mouse ever again.  a few months ago I was on the market for a VCard and there is one that caught my eye but then I deliberately decline to buy it because its Evga and bought one from MSI instead simply because I hate this mouse and have no faith in EVGA.  Yesterday I ordered a motherboard from Newegg for upgrade and I cross out all EVGA brand in search.  They have lost me as a customer, I think for good.  I don't care if they can fix the mouse issue tonight because I don't use it anymore and do not care anymore.  i suggest you guys do the same.