I have some beefy 15 inch tires that I plan on putting under my 2.5 RS once I get forester struts for it, but I know that the brakes are larger on the 2.5 RS than all the other imprezas of that generation.

 

What I don't know is, whether or not the brake assembly will be too big for 15 inch wheels.

 

I first did some broad googling to see if this was a common idea, but to no avail so I went a big deeper focusing on strictly major forums such as here, nasioc, rs25, etc. Still nothing answering my specific question. I did find a very nice write up on the brakes sizes for all major subarus here

Check this thread out: http://www.rs25.com/forums/f9/t161697-15-wheels-will-fit-over-stock-2000-2-5rs-brakes.html  

the dual piston calipers won't fit under 15" steel wheels.  

plenty of mid to late 90's legacy and outbacks (GT, LSi, OBW, SUS) got 15" aluminum wheels with larger dual piston calipers just like the RS and those aluminum rims will fit.

Awesome, thanks