Could early dreadnoughts be rearmed with 15-inch guns?

Would replacing 12-inch batteries in early dreadnoughts with fewer 15-inch guns keep them competitive?

Not very well: the larger shells are attractive, but a four-gun ship is poorly suited to the salvo-ranging methods the Royal Navy relied upon.

The answer accepts that a turret conversion might be physically imaginable, but argues that four heavy guns leave too little margin for effective ranging fire. Courageous, Glorious, and Furious are cautionary examples because the Royal Navy disliked the very small number of heavy guns imposed by their layouts. Observers normally needed at least three shell splashes to judge the fall of shot, and paired twin turrets made coordinated ranging salvos much easier than four independent single mounts. The larger shell therefore does not compensate for a battery that cannot support the fleet's preferred fire-control method.