A modern 15-inch/45 refit would be formidable but hypothetical

How would fully refitted Hood, Repulse, and King George V-class ships with 15-inch/50 guns change the balance?

They would be extremely dangerous, although the more plausible modern weapon at this date is a lighter 15-inch/45 rather than the earlier 15-inch/50 concept.

A fully modernized Hood, Repulse, or King George V-class battleship with improved 15-inch guns would be a formidable opponent. The proposed 15-inch/50 belonged to design work in the late 1910s and early 1920s. For the period under discussion, the alternative offered is a 15-inch/45. That design is described as lighter than the established 15-inch/42.