Extract from CAA LASORS
IR
The holder of a current and valid Instrument Rating Aeroplane (IR(A)) issued in accordance with ICAO Annex 1 by a non-JAA State may be issued with a JAR-FCL IR(A) providing the experience requirements as detailed in Section E1.2 have been met. Applicants must complete the following:
· Undertake IR theoretical knowledge instruction as determined by the Head of Training of an approved training provider.
· Pass all JAR-FCL theoretical knowledge examinations at IR level. Applicants who have passed JAR-FCL theoretical knowledge examinations at ATPL(A) level are exempted from this requirement.
· Complete a minimum of 15 hour instrument flying instruction (of which 5 hours may be in a FNPT 1 or 10 hours in a FNPT 2 or flight simulator.
· Complete any additional IR training considered necessary by the FTO
· Pass the 170A flight test
· Pass the IR(A) skill test (in accordance with Appendices 1 &2 to JAR-FCL 1.210) with a CAA Flight Examiner
Previous posts are quite right, it really is dependant on your previous experience. This states the minimum required hours for conversion. A good student could convert in 15 hours, a bad one.... who knows? Unfortunately an FTO cannot guess how much time you are going to need until they have flown with you at least once.
Also have you passed all 14 of the JAA examinations and do you already hold a JAA CPL? If not these also need to be looked at. I have replied to a more recent post with the details for CPL conversion. There are also a number of past posts on this topic, try a search for 'licence conversion' or alternatively 'Fogbound' as I have replied to a few of these posts answering the same questions.