My experience...I found that the suppressor with standard HV ammo was still noisy. Not a noticeable difference between my suppressed 15-22 and that of my friend with a non-suppressed 15-22 shooting right next to me. Then, I tried the Federal suppressor ammo. HUGE difference. All you could hear was the action cycling. THAT was what I was looking for.
Now, the pistols, the suppressor and standard velocity ammo, and other ammo was quiet. I just tried some CCI Quiet ammo yesterday, wouldn't cycle either the M&P22 or the Ruger SR22. Quiet, sure, but was a single shot experience. The pistols with standard velocity ammo and the suppressor ran fine, quiet and reliable. I haven't tried the Quiet CCI and 15-22 and suppressor yet, but have 4 mags filled with the Quiet, so will update soon.