Wow, to answer that, I need to kinda know how you plan on shooting the M&P 15/22 (again it's just a 22LR). But I may be able to help you in the right direction see below on the kind of setups you may want to do, and both won't hit your $1200 to $1500 budget range to boot:
1.) Tactical : Leave stock trigger, add Red Dot, front vertical grip or angle grip (Magpul), Magpul BUIS folding Iron sights, purchase CCI Tactical 22lr ammo, Compensator to aid in recoil.
2.) Hunting : Upgrade trigger to 3 lbs., 1X-4X or 3X-9X scope, CCI Tactical 22lr ammo, Jerry Miculek compensator adds weight and helps a little on recoil (also looks cool).
Have fun tricking out the M&P, it was the highlite of my fun for sure.
Keepem in the Xring.