Factory recommended tire size is 6.00x16 front and rear. Or 6.50x16 on the rear, for 4.700 lbs. GVW.
Something to keep in mind, a wide wheel/tire combo on the front exerts a lot of stress on the steering box mount and can cause them to crack around the mounting bolt holes from flex (fairly common).
I'm using 16"x4.5" wheels all around, with 6.00x16 tires on the front and 7.00x16's on the rear. I went to this size on the rear to keep my gear ratio where I wanted it using the taller rear tire, for a bit of rubber rake with the factory ride height, and a slightly bigger contact patch to help with traction (hot rod
The 16"x4.5" wheels and 6.00x16 tires on the front help to keep the stress down on the steering components, due to the wheel's shorter backspace and tire's smaller contact patch, while filling the wheel opening for a better look.
It's my opinion, 15" wheel/tire combos look out of place on these trucks, unless the suspension has been lowered, helping to fill the fender opening.
Just my two cents worth....