The answer is, find another wheel. One of the big advantages of having a 4.50" bolt pattern is that there are hundreds of different wheels available. 15x7 with 4.00"-4.50" backspacing is not hard to find.
Yeah that's not an ideal backspace for a 7" wheel at all, your best bet would be to pick something with at least a 4" backspace. And ideally more like 4.25 or 4.5".
With a 15x7 and 3.75" of backspace you could run up to a 205/65/15, but that would be the absolute max width tire you could run and it would be tight, some cars might need some minor adjustments to the lower fender braces. That's assuming you've got BBP brakes. Stock SBP brakes would give you a little more room, but I'm not sure it would be enough to run a 215.
