Guns used in single coastal artillery mountings (BSG) in Denmark had very little power assist and were hand rammed. They are said to have had a ROF of one shot every 70 seconds. The twin mountings originally intended for Gneisenau but allocated for Denmark coastal defense would have had a ROF similar to the ships.
Yeah, due to size and weight restriction, neither Gnes, sevastapol or if it had ever happened, Scharn would have been able to have the power assisted loading. It wouldnt fit. Which means it would have likely had the same relaod as the coastal batteries
but probably worse if dealing with the rolling of the ship, etc.
So the fact they currently have the same reload as Bismark, is a total work of fiction
Gneisenau had had its bow blown apart by an RAF bomb that exploded the ammunition - apparently it would have taken longer to repair than to rebuild with 15" guns - dunno how that works, but it is repeated in many places.