So reading this and the other thread about the charging handles in the 15-22, I began to get curious as to the differences myself. I have therefor done some super scientific research and came up with the following:
The only difference that I can see is that the latch on the 15-22 is longer at the "hook" end. Note the 15-22 handle on the right compared to a standard AR15 charging handle on the left.
And when latches are out of the charging handle (15-22 on the left, sorry for the inconsistency).
The reason the latch is longer on the 15-22 is because it is designed to hook over a "bump" on the upper receiver (top 2 pictures), where as an AR15 latch hooks into a recess in the same spot (bottom 2 pictures):
I put an AR15 latch onto a 15-22 handle, and found it isn't long enough to go over the bump.
Theoretically, you could turn the "outie" of the 15-22 into an "innie" with a little bit of filing and get a standard AR15 latch to work.
P.S. Sorry for the dog hairs in the photos. Apparently they are everywhere!