Replacing six 18-inch guns with triple 15-inch turrets

How many triple turrets would a proposed 15-inch alternative to six 18-inch guns use?

Three triple turrets, giving nine 15-inch guns, unless the entire design changed substantially.

Three triple 15-inch turrets are the proposed alternative to six 18-inch guns. That gives nine guns without a wholesale change to the design. The ship's name is unclear in the captions.