Kodiak Island,
Somewhat reluctant to reply as I don't like dissing other's choices in guns, if it works for them it's all good...
However, I wouldn't spend the $200 on a tax stamp for the S&W 15-22, because I'm not a fan of the plastic construction and from the reviews I've read (no personal experience) the accuracy seems not to be that good.
I had (now my daughters) a Tippman AR-22. If I was going to SBR an AR-15/22, it presently would be my choice... As the accuracy is decent (with the factory barrel), it is similar to the AR-15 in operation with last round bolt hold open, etc and there is 'some' interchangeability of AR15 parts (safety, trigger, stocks, forends, etc.).
I am going to SBR a 10/22... after I decide which receiver I want.
Jerry
Tippman AR-22, Ten shots at 50 yards, CCI Standard Velocity, the square is one inch;