is a 120 m and 32000 tons beast, almost the weight of Titanic, not an attack sub, that is her time to submerge
if you want do it faster go to data/submarine/yoursub/, find the .sim file, open him with sil3nt editor and increase ballast tanks flood speed
Not too much because you will have funny efects like a sub swimming like a dolphin or going down like a rock
