IMHO, none of the problems you are having are the result of a polymer lower. As for "****** polymer" the overwhelming majority of semi-automatic pistols on the market are polymer-framed and they seem to do quite well.

You knew the 15-22 had polymer upper and lower receivers when you bought it. If you wanted aluminum uppers and lowers, you should have bought an AR and put a .22 conversion on it in the first place.

Just my opinion, of course.