Is that on the front? back? or both? I have 15x7's with 4 1/2 inch back spacing on the front and 15x8's on the back with no problem with original drum brakes front and back. There may be some other restrictions if you have disc brakes. Also, what size tires are you putting on them?
15x7.5 may be a little tight on the front depending on what size tires you put on. should be no problem on the back. You may have to stay with a 235/60 or smaller on the front or else it will start rubbing the fenders during turns. As long as you have stock springs on the back, it should be clear. I am running 265/50's on the back of my 69.