As I stated above, I originally misspoke, and was referring to the Courageous class of cruisers. And yes, they had 15" guns, 4 of them, mounted in pairs.
In the 20's, HMS Courageous was converted to an aircraft carrier, much like Furious. Furious had been intended to be the third ship in the class, but later changed and purpose-built as a carrier.
https://en.wikipedia.org/wiki/HMS_Courageous_(50)
I originally started working with Avalanche Press' WWI games, but utlimately decided to do a straight conversion from the specs, rather than baking in someone else's assumptions.