Short answer, Yes. They are only similar in name. I'm not a fan of either, but had plenty of guitars with both.
The 8515S are my very definition of meh. Don't really excel at much and don't fail at much either. All in all not bad but not great. Some people like them, I don't, but there is worse out there.
The US 8515 are probably the most clear and articulate pickups I've ever played. Too much for me personally, if that's a thing. They are on the modern side of things and do most things well if not great. The neck is tops in terms of PRS pickups, but the bridge is lacking to me. Pairs amazing with the \m/ bridge, which rocks and very versatile.
There is a noticeable difference to the core versions of imports. Your ears and S2 will luv you for it. Happy modding.