Why not keep 15-inch guns?

If the Royal Navy won Jutland with 15-inch guns, why would it not keep that calibre for the next generation?

Foreign 16-inch programmes would still drive growth, and a 16.5-inch gun offered a plausible British balance between greater hitting power and a practical rate of fire.

Foreign construction would keep pressure on British gun size even after a successful Jutland. The United States and other powers were already considering 16-inch or larger weapons, so retaining 15 inches would surrender part of the competitive benchmark. The projected 16.5-inch G3 weapon offers a plausible compromise because it could fire heavier shells without the slower rate associated with an 18-inch gun. Tactical lessons from close-range fighting therefore meet the industrial logic of the postwar naval arms race.