The actual maximum ship size that can be jumped is the tonnage of the jump ship. The jump drive has to exceed the jump ship's tonnage to function, but otherwise has no impact on max tonnage. In this case you're trying to jump a 2000ton ship with a 1500ton max.
So for example, if you put that same jump drive in a 3000 ton vessel, it would have a 3000ton jump max. If you put it in a 4000 ton vessel, it'd have a 4000ton jump max. If you put it in a 4050 ton vessel, the ship would be unable to jump itself.