Purchased the Z20 & Z15 keyboards and the Torq X5 & X17 mice.  Package arrived today.
 
Z20 & Z15
We like both models.  Wife unboxed & claimed the Z20 before I even came in the room!  She likes it equal to her Corsair K70 MKII RGB black model.  I have the Corsair K70 MKII SE white edition & a Roccat Ryos TKL.  I actually prefer the Z15 to all of the keyboards I have ever used up to this point.  The Z15 keys are quieter then the Z20 and the volume wheel is easier to spin when compared to the Z20 or the Corsair K70 (might just be random chance, and each physical keyboard might have different tension on the wheel right from the factory?). 
 
Installed the EVGA keyboard software without issues on both computers.  Not a fan of RGB on anything, so the only thing we did with the software was set the lighting to one color and dimmed it to about 15%.  Was very easy and straightforward.  Compared to the Roccat software, EVGAs is awesome.  Key presses actuate quickly and accurately so far. on both keyboards  My Roccat keyboard makes my pinky go numb holding shift to sprint in games.  These new keys that require less force to actuate are a finger saver.  Side note: it appears the keyboard is set to 6 key rollover by default instead of N key.    

Lion99999
Purchased the Z20 & Z15 keyboards and the Torq X5 & X17 mice.  Package arrived today.
 
Z20 & Z15
We like both models.  Wife unboxed & claimed the Z20 before I even came in the room!  She likes it equal to her Corsair K70 MKII RGB black model.  I have the Corsair K70 MKII SE white edition & a Roccat Ryos TKL.  I actually prefer the Z15 to all of the keyboards I have ever used up to this point.  The Z15 keys are quieter then the Z20 and the volume wheel is easier to spin when compared to the Z20 or the Corsair K70 (might just be random chance, and each physical keyboard might have different tension on the wheel right from the factory?). 
 
Installed the EVGA keyboard software without issues on both computers.  Not a fan of RGB on anything, so the only thing we did with the software was set the lighting to one color and dimmed it to about 15%.  Was very easy and straightforward.  Compared to the Roccat software, EVGAs is awesome.  Key presses actuate quickly and accurately so far. on both keyboards  My Roccat keyboard makes my pinky go numb holding shift to sprint in games.  These new keys that require less force to actuate are a finger saver.  Side note: it appears the keyboard is set to 6 key rollover by default instead of N key.    

Did you get the clicky or linear?  I got a 20 clickly and i like it, but want to change out my work keyboard so i was debating just getting another z20 clicky or trying the 15.
 
what do you like more about the 15 vs the 20?

Hoggle
I personally like the Z20 more but both are good options. I don’t mind RGB but mostly like you the ability to select a single color so I like the light bars. Also I like the fact that the the TIme of Flight sensor can put the computer to sleep. Since my girlfriend works with student records at a university so having the ability to log her out when she leaves for lunch adds extra security. But for gaming both are good and I love the feeling of the mechanical keys. They are a joy to use and respond so quickly. As for the 6 key rollover vs. N Key rollover it’s a moot point at the 4000 report rate. That would be like hitting over 24 keys every millisecond. No going to really be an issue unless someone sets the response rate to 1000.

RGB i just set to white on anything :)
 
i'm coming from Corsair MK70's with reds/browns.  I do like the z20 clicky but not sure if i should branch out to try the z15 with kalih's or stick to the optical switches and then maybe try the linears....  though the promo expired so that kinda sucks.

@Jlmajeske: I purchased the linear versions. 
Z15 Advantages according to my "non scientific" and "minimal investment of time":
- The Z15 seems quieter then the Z20 to my ears while typing
- I prefer the way the Z15 keys feel.  I type fast and the Z15 feels smoother to me.
- Z15 is less wide (17.5" wide) vs the Z20 (18 5/8" wide)..ok that was semi scientific, I actually used a tape measure
- Z15 has no macro buttons which I would never use anyway, saving cost
- Z15 has no TOF sensor which I wouldn't use anyway thereby reducing cost and complexity, and increasing reliability (my theory)
- Z15 doesnt have an audio 3.5mm cord for headset plug on keyboard, nor an extra usb cord = less annoying bulk across desk.  I use a 2.1 desk system (poor man's audio flex: Denon AVR + Fluance bookshelves + Crown XLS2000 + Alpine Type R 12" in a vented 4.6cu ft vented box & a 12" Infinity in a 4.6cu ft vented box)
 
Side notes:
- both keyboards are very heavy which I LOVE!  The keyboards stay in place and don't get easily pushed around.
- I do sometimes accidentally hold down movement keys while gaming and get confused why my toon is apparently strafing when he should be running straight.  It is due to these awesome, easy to actuate keys (larger hands and I lazily rest them on the keys - mid 40s year old you become, movements on accident you will do...if Yoda was a gamer, he might just say such a thing)  
- the 6 key rollover vs n key rollover I only came across because I duck duck go'd n key rollover for some insight.  Found a site that you click in the box and hold down a metric fuq ton of keys and see if they all register.  By default it was set to 6 key.  The whole polling at 4k vs 1k makes sense.  Nobody would probably ever notice.  On the other hand, if you bought a car with a supercharger or turbo, and found out by default its set to off, you would probably find that odd.  Spend the money to engineer, build, & source the extra hardware necessary for every key to be able to be pressed at the same time and it would be communicated to the computer, at extra cost, but then ship it set to OFF by default seems odd.  I did find some articles explainig that older BIOS versions can only see 6 key rollover or something to that effect and n key rollover could cause the keyboard to not be visible or something.  Didn't apply to me so I stopped trying to decipher the details.
  

Batboygotoj
Have you guys had experience with Corsair K70 Cherry mx switch, would you recommend the EVGA Z15 over Corsair?

I have the K70 MK.2 SE Rapidfire - very good keyboard. 
 
Haven't gotten my hands on the Z15 but I plan to order one. 

if only they offered the 50% to non elite lol I'd want to buy the keyboard/mouse from them