The 15rd version has a shorter magazine well to accommodate Glock 19 magazines (It will accept Glock 19 15rd or Glock 17 higher capacity magazines including the longer 33rd magazines and Drums. The Glock 17 version rifle has a longer magazine well for accepting Glock 17 or higher capacity magazines and drums as well. The Glock 17 rifle will not accept the shorter Glock 19 15rd magazines as they are simply too short.

Glock 17 and Glock 22 won’t take Glock 19 or Glock 23 magazines. They are shorter. But backwards they will fit. Even the big mags.

Yes not much difference as long as the mags are the same length and stack.