[Big Dave]

Stay with the 12 inchers.

Rolling resistance is peanuts compared to rotational inertia, especially for city driving.

Every time you accelerate or decelerate (regardless of how gently) you actually accelerate the wheels and tires which them transfer motion to the road. That acceleration is resisted by rotational inertia.

Rotational inertia increases with the square of the diameter. Less inertia means less energy goes into accelerating those four "flywheels" that hold you off the road.

Double the diameter and the inertia goes up four times.

From a practical standpoint it is getting harder to find 12, 13, and 14 inch tires these days.