Would a larger Royal Navy deter German surface construction?

Would Germany still attempt a surface-fleet buildup if the Royal Navy had twenty-five active capital ships?

Yes. Germany already faced a large British numerical lead, and its response to French construction would still give it reasons to build.

A larger British fleet is unlikely to stop German surface-warship construction in this scenario. Germany would already be starting far behind whether Britain possessed fifteen or twenty-five capital ships. Scharnhorst's immediate design competition is identified as French, so the French fleet remains part of the German calculation. France's ten-ship allowance could encourage completion of Normandie-class battleships alongside older Courbet and Bretagne ships. Several combinations are considered, and Bearn could still become a carrier if France completed fewer Normandie hulls as battleships.