Shunter, you sound like a happy person!
It is true that you only need 15 hours, but is that realistic for most people? Although I would not argue that the JAA IR is much harder, it is rather different and the airspace in Europe works a bit differently.
My point here is that it would be prudent to anticipate that you could need significantly more than the absolute minimum of 5 hours of twin and 10 hours of sim. I know a few who found themselves in that situation, the conversion cost was not far from the full JAA IR.