Once you get bigger than 33s you generally buy different wheels anyways, so why not go to 16s or even 17s? Then you can get the metric equivalent of 35 inch duratracs. My 33s are on stock wheels, but they really need to be on some wider aftermarket wheels with less backspacing.
id stay with 15s going 16 or 17 means more
and the load range would be different.