I actually own both at this moment and will probably keep them for right now. I've only owned them for a couple weeks.
The 416 is heavier and feels more like the real thing. The 15-22 is easier to clean thoroughly. The 416 manual says to only strip the gun to a certain point or you void the warranty. Not sure how much residue would have to accumulate before having issues. It's pretty easy to clean the upper.
The 416 doesn't have a bolt hold open like the 15-22. Available mags are 10, 20, and 30 rounders. 30 rounders are $60 right now. The trigger on the my 416 is not quite as smooth as the 15-22.
I have 500 rounds through both of them and they both shoot nice.
Half my buddy's like the 416 better, the other half like the 15-22.
I'd say if you have either one, you've got a nice gun.