I use Troy, KAC, and Magpul Pro's on various AR builds, but am using a no-name metal folding set from Amazon on the 15-22. They are "styled" like the troy's essentially, with HK style front. You' have to replace the mounting screw, but for the money they are hard to beat, imo on a range plinker 22.
[ame="http://www.amazon.com/Trinity-Force-Sight-front-Mount/dp/B00MJKOK28/ref=sr_1_1?ie=UTF8&qid=1428203527&sr=8-1&keywords=trinity+force+sight"]Amazon.com : Trinity Force Flip Up Iron Sight Rear/front Sight Mount : Sports & Outdoors@@AMEPARAM@@http://ecx.images-amazon.com/images/I/41N0YPTyezL.@@AMEPARAM@@41N0YPTyezL[/ame]