After many months, finally got my "hall pass" (ATF approval paperwork) for my GemTech Outback IID suppressor.
For the 15-22, a couple of things to note: get the spacer from GemTech, remove the flash hider and the crush washer, then install the spacer. Do not use the crush washer when installing the suppressor (advice from GemTech).
Sounds sorta like an electric stapler when using. Very pleased, just the wait was way too long.