I have had and shot two different AR 15 22 Lr conversions. The first was a Chiappa polymer 22 Lr upper, I will add the mags that came with it are very poor. After I added Black Dog manufactured mags, this upper shot any ammo and was surprisingly accurate. I did have a failure with the upper receiver after a couple of years and 10s of thousands of rounds. That was no big deal, I just took all the parts and put them on a Rockriver stripped upper and after over 7 years and 100s of thousands of rounds, it still shoots very well.
The second was a purpose built for my granddaughter. Aero upper and lower with a Tactical Solutions barrel and bolt kit. This one was a very light weight with the barrel being a SS tube with aluminum outer, and it was a tack driver... very accurate.
There are a couple of AR 15 22 Lr. Conversions out there. But I am not a fan of a kit that only is a bolt and chamber, shooting through a 556 or 223 barrel.
Also if the upper will fit on your AR 15 lower, that is a plus. The Colt, and S&W are complete stand alone guns, the upper will not work on a standard AR.
I very much like being able to use my lower for 22 Lr. or 223 with just an upper and mag change.
CMMG and Core where selling Complete uppers and there are still barrels and bolts from CMMG that make outstanding 22 Lr. AR 15 uppers. And at one time RockRiver arms was listing a 22Lr upper.