What is the widest tire that will fit on a 5.5" x 15 rim? Everything I have found points to somewhere between 205 and 215. This is for a buggy so fender interferance is not a problem.
The minimum recommended rim width for a 205 is 5.5", for a 215 it's 6.0". Either size would be better off on a rim an inch wider than that; IMO, the "right" size for a 5.5" rim would be a 175 or 185, but 205 would be acceptable.