Balancing armor on a 9.2-inch treaty cruiser

Is a 4.5-5.5-inch belt, 2.5-inch deck, and 2-inch turret armor reasonable for a 15,500-ton cruiser with 9.2-inch guns?

Broadly yes, with a 4.5-inch belt and roughly 2.5-3 inches of deck protection, while spare plate could reinforce turret faces, sides, and roofs.

The proposed scheme is a workable baseline for the displacement. After the belt and deck requirements were met, available plate would likely be concentrated around the forward faces and exposed sides of the turrets.