Why British 15-inch/50 development stalled

Could the Royal Navy have continued developing 15-inch/50 guns for later capital ships?

Yes technically, but Treasury funding and the Ten Year Rule made continued development unlikely.

The technical route to a 15-inch/50 weapon was available, and such guns could have armed later Queen Elizabeth derivatives, battleships, or battlecruisers. The decisive obstacle was not metallurgy or naval architecture but money. Interwar planning assumed that Britain would not face a major war for ten years, allowing the Treasury to defer expensive weapons development. Fiscal doctrine can therefore close an otherwise feasible design path.