Could Britain lengthen the 15-inch gun during refits?

Should Britain have upgraded its 15-inch guns from 42 to 45 calibres during interwar refits?

It was technically interesting and probably possible, but treaty rules might have limited such a main-armament change.

Lengthening the familiar British 15-inch weapon could increase performance without adopting an entirely new calibre. The engineering possibility was only part of the decision. Treaty language might restrict changes to main armament even when nominal bore diameter stayed the same. Modernization programmes had to satisfy ballistics, industrial cost, and legal interpretation together.