Coastal 15-inch guns would not make Spanish battleships straightforward

Could Spain use coastal 15-inch guns to build three battleships if the planned Littorio-derived ships were abandoned?

Probably not as a straightforward programme: the coastal weapons might not suit shipboard use, spare barrels were limited, and Spain's wider constraints made new battleships doubtful.

The coastal weapons did not provide a ready-made battleship armament. Their mountings and guns were not necessarily suitable for shipboard use, and enough spare barrels may not have existed. Spain's broader industrial and financial difficulties would still constrain any attempt to build the hulls. A gun inventory does not create the shipbuilding system needed to turn those weapons into battleships.