I know very happy owners of both the 522 and the 15-22.
Both guns have had their problems:
15-22: some early guns suffered FTF/FTE issues which appear to have been resolved with updated springs, extractor components and magazines.
522: recoil spring guide e-clips failing repeatedly, causing damaged springs. I've heard that while some owners have come up with their own fixes, Sig tech support just has as supply of replacement springs and e-clips.
These issues aside, both guns will consume copious amounts of rimfire ammo and tear large ragged holes in targets of all kinds, while making their owners grin from ear-to-ear.
My personal preference is the 15-22, but that's just me