7.00-15 is 29". 7" sidewall (times 2) + 15" wheel. To get in the 30" range you end up with tires that are very wide, like the 31x10.50R15 LT. This is 30.4" tire with a 10.9" width.
I went to 16" rims and a 7.50R16 which is a 31" tire. Find a locally owned tire shop that does truck tires, they might be able to help in your selection.
