So unless you do the IMC rating with a dual rated Instructor (FAA & JAA)
it's 40 hrs and not 25.
No it's not. The 40hrs are any instrument time with any kind of instructor, or solo, or simulated-instrument time logged with a non-instructor safety-pilot.
So the "conceivable minimum" is 15hrs IMC training, 22hrs instrument time post-IMC (actual solo or simulated, wearing foggles with a safety pilot) and 3hrs with an FAA IR instructor. The IMC training counts towards the 15hrs as long as the instructor was an IR instructor (although sometimes interpretations differ). It's not even clear that the 3hrs has to be with an FAA CFII, olny sufficient time for you to be signed-off for a checkride, although it's difficult to imagine anyone signing a pilot off with less than 3hrs.