Those will take a 275/60/15, but they won't fit. Not enough backspacing for a 15x8.5". You'd need at least 4.75" backspace on an 8.5" rim.
275/60/15's will work on an 15x8, and on a SBP 8 3/4 you could get away with about 4.5" of backspace. 275's are about as big as you can go though with the stock spring locations and unaltered quarter lips.
