If I'm not mistaken, operation wise the only difference (in terms of "user interface) is that there's no bolt hold open feature after the last shot's been fired. Other than that, if my research was worth anything, not really. Mechanically, SU-16 is gas operated while the SU-22 is a blow-back design so under the covers they will be pretty different
The "gas tube" on the 22 is shorter than on the SU16, which you can see if you compare an SU22 and SU16 side by side. This means you can't use the 16's forend bipod and the sight radius is shorter.
The SU22 uses the SU16C sights, so the front sight is at the front of the recoil spring tube (which corresponds to the piston tube of the -16) rather than on a tower at the muzzle.
Actually, the SU22 does have a bolt latch*, but it's not activated by the .22cal magazine follower. The follower itself holds the bolt open after the last shot, but when the mag is removed, the bolt will snap closed. To use the rifle's integral bolt latch, you have to pull the bolt all the way back by hand, then push the latch up, same as on the SU16.
*Since both rifles use the same receiver, the hold-open was left in place (at least on my SU22).