I think I have a 3-9 Nikon Rimfire on my M&P15-22 but if you're shooting steel matches with it I agree with the others about a 1X - 4,6,8 LPVO. I've never researched them by weight so can't help you there. My only experience with LPVO's is with Vortex and Leupold. The Vortex Strike Eagles are very good optics for the money and you can't beat the warranty. My Leupold was far more expensive but a great optic.
If I had the money I'd get a Vortex Razor but that's way overkill for a M&P15-22. I'd suggest looking at the Strike Eagles and combining it with a lightweight mount.