Another tire thread! Need some new tires for 15" rims

Since you are staying with 15" I recommend MAXXIS ST225/75R15-D or E.
I would probably get the E rated. Check the wheel rating to determine if you can run 80psi.

Marathon does not seem to have an E in this size.

http://www.maxxis.com/catalog/tire-122-129-st-radial-m8008

Discount tire should be able to order them in for install.
http://locator.discounttire.com/