Just make sure you don't go over the ~9.5" width or you will rub the frame

 

You should be fine with a 245/75/15, but realize that it is outside of factory specifications, so your mileage will vary depending on a number of other factors like how much your 13 year old factory suspension is sagging.

 

So if I run a 30x9.5x15 I'll still be OK?
The exact numbers are 29.1x9.50x15 for grabber at2's. I'd like the extra tire that offers over the 235/75/15