I'd go to a 235 55 15 in back, and maybe 205 60 15 in front, with 6" wide wheels in front and 7" wide in back. that's what I got when I tried calculating the 235 width tire with a 15" wheel for the back using the tire height of our mustang for reference, and the front tires mentioned are less than 1/2" shorter than the rear
unless you want to just use the same tires in front as back, then I'd just use the 235 55's all around on 7-8" wide wheels(235 is about a 9" wide tire). the 235 60 14's on our stang fit fine, so that's why I was using that width for calculating
just don't do what the previous owner of ours did and go with the 235 60 14's all around, but with 6" wide wheels in front and 7" in rear... 6" wheels are a bit narrow for the 235, causes a bit of sidewall roll