If you do end up having issues with the spring not providing enough power you can try to add spacers to the rod it sits on.

I'm not sure if during recoil the spring binds, but if not than any extra room taken up by a small washer or something similar will increase compression and give you a little bit more resistance.

You also might be able to call a company like Wolff that makes a ton of different springs and see if they have something very similar. I doubt S&W makes their own springs, but I have no idea who the OEM would be for the 15-22.