Are the slides on the above SIGs interchangeable?
Tried the P228 slide on the P225 and it seemed to fit.

I Know the 228 slide will fit on a 229 frame as that is the set up I am running on my 229 40 frame since traded my 40 upper for a 228 upper and it runs great.

From my experience the 229 upper will not fit on a 228 frame as i tired it and it would not fit right. I never even tried to run it as i di not want to mess anything up as it was not my 228 frame it was a friends that we were trying to see if it would work.

I don't know about the 225 slide as I never owned one. I would take a guess and say that it might fit but might not run like it should. I am sure someone else will be along let you know for sure.