re front rotors.

12” is about the max rotor diameter for 15” wheels. And at the max the caliper and wheel design factor in too, so it can depend on the particular brake kit and wheel.

The largest Mopar set up for the 15’s is the 11.75’s from the 76-81 B and R bodies. I think wilwood has a 12” kit that fits most 15” wheels but what kit is available depends on what spindle you’ve got. The base wilwood kit uses 11” rotors. Better brakes out there for the money.