Great choice on the 15/22 and may i give you some summed up advice as an owner of one myself.
Do NOT shoot any Remington ammo of any sorts threw this gun, Out of battery discharges have been proven especially with this ammo. This info came straight from S&W. It was worse when the gun was new on the market, But S&W is quickly updating the gun with fixs.
Take your time loading the mags one round at a time and watch to make sure they are staggered properly. If not you will get stove pipes but with a live round mangled in the mag.
The gun LOVES Federal bulk of any sort, Great since Walmart always has it now.
Its even decently accurate with it. I can do 2" groups at 50 yards wich is good with bulk ammo and a semi auto.
Subsonic ammo is your friend for accuracy. My 15/22 can do 1" and sub 1" 3 round groups with subsonic ammo at 50 yards.
1" was with Aguila SniperSubSonic 60gr
Sub 1" was with CCI subsonic hollow points.
I have more ammo to test and further distances yet so it could get better or worse, But i plan to get the best results i can at 100 yards which wont be easy.
The gun also responds well to the 15 minute trigger job and lightens the pull too around 4lbs
Here is a link to the S&W forums with a 15/22 section just for this gun.
http://smith-wessonforum.com/smith-wesson-m-p-15-22/
I cant think of any more tips.
If you have any questions you can pm me anytime and i can either give an answer or tell you who can.
I love mine and besides a few jambs due to me loading the mags in a hurry its been flawless.