I've got the Primary Arms on my 15-22 and am very happy with it.
For the price, (under $80 delivered, including mount), it was the best bang for the buck. In FL, on light sand or a white target, on a bright day, the dot can be sometimes hard to pick up. However, for the 99% of the time, it is just fine. The mount you see here will co-witness fine on an absolute co-witness for the "fixed" sights. For the Magpul PTS flip ups, the co-witness is about a lower 1/3 co-witness.
For the next price up, I would look at the Bushness TRS25 (I think the number is). A little more than that is the Vortex Bright Red Dot. (The two color sight is a little less bright than the single bright red). And, for the upper range closer to the $200 is the Lucid HS7 that has a great reputation.
For the 15-22?? I think the Primary Arms would do everything you need for a great price.
In comparison, I have an Aimpoint PRO on my "full size" AR. The Primary Arms is nowhere near as bright.... but was not going to spend as much on the sight as I did on the rifle.
Have a great time with the S&W 15-22!!!!