The reason NSM won't work with 1.5 is that new ship types were introduced for that version. All the old types will sink in an NSM-like manner. If you run into one of the new ships, they will sink in stock manner. Nothing will explode and your game will not crash.
There's no reason not to try NSM with 1.5 and see if you like it!
However, if you don't like the way ships sink in RFB, that's exactly the effect of NSM too. You have to punch enough holes in different places to flood the target in order to sink it. If you hit the same spot with four torpedoes you're probably not going to sink it.