Plug your keyboard directly to the motherboard's I/O USB ports in the back. 

make sure that you install Unleash RGB to make sure that the firmware is updated on the Z15. Once firmware is updated test again and if possible test on a different computer. 

I sent my keyboard back to EVGA and completed the RMA process. Received a new one and the problem still persists. It must be a setting somewhere. Here is what I did:
1. Disabled legacy usb support under BIOS,
2. Unchecked "Allow the computer to turn of this device to save power" in Power Management tab for all USB Root Hubs (USB 3.0) at device manager.
 
Still having the same issue. 

Kbird666
I have the same Issue with my new Z15 , no issues whatsoever with the previous Steel series KB on my Z590 MB and with the number of reports here on the Forum with the same issue my guess is it is a Firmware Issue with the KB, I keep getting the Device Descriptor Request Failed error  and have to climb under my desk and unplug/plug it again which is a major PITA.

The KB also seems to ignore the system and Unleashed repeat and repeat delay settings I am getting a lot of repeated
keys at all polling rates.
 

 
So looks like I have found the solution for my problem. I thoroughly looked all the BIOS settings and clicked Advanced Settings -> Wake up event Setup -> Enable Wake on USB device, changed Wake Up Event from "OS" to "BIOS". Now, each time I hibernate or reboot, my keyboard works! Hope this will help you also. 

It's really sad to see that this issue has never been solved and there are a lot of identical threads all over the internet.
I would like to add another piece of information to this so maybe then EVGA can solve the issue.
When the computer boots and the keyboard doesn't turn on, I noticed that in EVGA Unleash software the report rate is set 4000 Hz, even though I always had it at 1000 Hz.
Switching to 1000 Hz makes the keyboard turn on.
Any suggestions, maybe a firmware rollback or something? Maybe push a firmware update which doesn't force you the keyboard to 4000 Hz when it's turned off?

straussy

adsubzero
It's really sad to see that this issue has never been solved and there are a lot of identical threads all over the internet.
I would like to add another piece of information to this so maybe then EVGA can solve the issue.
When the computer boots and the keyboard doesn't turn on, I noticed that in EVGA Unleash software the report rate is set 4000 Hz, even though I always had it at 1000 Hz.
Switching to 1000 Hz makes the keyboard turn on.
Any suggestions, maybe a firmware rollback or something? Maybe push a firmware update which doesn't force you the keyboard to 4000 Hz when it's turned off?

I can confirm the exact problem mentioned above with my Z15 @ boot. I have reflashed the Bios connected different keyboards to confirm  MY PC is not the problem EVGA you need to fix this!!!
Or at least provide a way to roll back firmware if this company is not capable of performing the firmware tweaks that are required!! 
Its sad to see this company on a downhill trend!!!

Sadly I can't return the keyboard, so I'm stuck for now in hopes of them fixing something. However, seeing posts from TWO YEARS AGO talking about the same issue I doubt anything will change. This belongs in the trash. 90% of the time it doesn't turn on at boot. It's beyond annoying. Fix your damn issues and acknowledge the problem EVGA!

I was also reading you can adjust what devices go into sleep mode to save power and disable the keyboard from going into sleep mode. This won’t help on a boot up but will help if the Z-15 goes to sleep and doesn’t want to wake up without being unplugged.