Hi NE...
If I'm not mistaken you are playing with TWoS , right?
All crew abilities in TWoS are tuned not to produce any significant unrealistic effect. Some abilities are even removed, like overcharge electric engines, repair destroyed items ect...
Now, this information about 10min per tube is somewhat surprising for me because, during my research, I found on several places that it will take more than 1h to reload all 4 tubes. There were also many more factors involved in torpedoes reloading speeds like, crew skill, sea state, submarine longitudinal axis angle ect... Therefore, I think 20 min for trained crew is pretty much realistic time...
Gap?