all of them had 280kg of explosive, as pretty much all the torps after the TII were just varients of the same torp.
they just improved the homing or running ability of each torp by replacing the seaker head/detonator, batteries and motor. this left the same explosive throughout.
the american torps varies wildly though as they experimented with allsorts of different heads and whatnot.
the mk15 was actually lighter yet packed 375kg of torpex
the mk18 was actually a copy of the german G7e after a couple ran ashore and only carried 280kg of torpex but it was electric so they needed the extra room for the batteries and whatnot.
all of which can be wiki'd btw i'm just sad enough to know a fair bit and have lots of links...