There is nothing special about the current american standard battleships that forces them to have a 40 second reload. This is just an unnecessarily long reload time and unfair now that the Japanese Mutsu gets its absolute peak RoF of 24 seconds. Not to mention the other 15" weapons with 26 second reload times.
Navweps gives standard battleships such as Nevada a peak rate of fire of 1.75 rounds per minute, thats 35 seconds. This is not game breaking at the slightest but only serve to make the 14" standards at least playable with all the sub 30 second reload battleships sailing around.