You need to measure the backspacing of your wheels or you could have rubbing from lack of clearance, even with a narrow tire. If you have the spacing that I have, you can go with P235 60 R15's & be okay. I have a '71 Scamp running with 15x7 small bolt, rally wheels from Wheel Vintiques.
It's been years since I bought mine so I'd have to check the order in my file, but I believe the backspacing they made for me is 4-1/2" or maybe 4-3/4". The P235 60 R15's are on all four wheels & have never had a clearance issue front or rear when turning, hitting bumps & dips, or having passengers.