"I only need to 15 hours flying and 30 ground as I have an FAA CFI rating"
Not quite true, what you mean is that you have to do at least " 15 and 30" There is no credit in JAR-FCL for non JAA FI ratings . As a concession the CAA base their requirements on App 1 to JAR-FCL 1.300 which states: you must have 500 hours of flight time of which 200 shall be as a flight instructor, then it goes on to say:
have completed in accordance with JAR-FCL the approved relevant course of theoretical instruction and flight training. (JAR FCL 1.340) The course may be modified, as approved by the Authority, taking into account the previous training and experience, but shall comprise at least 30 hours of ground instruction and 15 hours flight instruction.
http://www.jaa.nl/publications/jars/541268.pdf
So the 15 and 30 is dependant upon your previous experience and the FIC Instructor recomending you for test at that point. It is not guaranteed.