Not
quite that simple....
The method of attaining an IR(A) following this modular course is competency-based. However, the minimum requirements below shall be completed by the applicant. Additional training may be required to reach required competencies.
(a) A single-engine competency-based modular IR(A) course shall include at least 40 hours of instrument time under instruction, of which up to 10 hours may be instrument ground time in an FNPT I, or up to 25 hours in an FFS or FNPT II. A maximum of 5 hours of FNPT II or FFS instrument ground time may be conducted in an FNPT I.
(i) When the applicant has:
(A) completed instrument flight instruction provided by an IRI(A) or an FI(A) holding the privilege to provide training for the IR; or
(B) prior flight time under IFR as PIC on aeroplanes, under a rating providing the privileges to fly under IFR and in IMC
these hours may be credited towards the 40 hours above up to maximum of 30 hours,
(ii) When the applicant has prior instrument flight time under instruction other than specified in point (a)(i), these hours may be credited towards the required 40 hours up to a maximum of 15 hours.
(iii) In any case, the flying training shall include at least 10 hours of instrument flight time under instruction in an aeroplane at an ATO.
(iv) The total amount of dual instrument instruction shall not be less than 25 hours.
rudestuff, under your plan, if you didn't complete you FAA IR, you would only be credited with up to 15 hours of dual instrument flight time under instruction. If you didn't have any other instrument qualification enabling you to record PIC flight time under IFR (note - this doesn't include VFR PPL holders claiming 'IFR' as the requirement means that such time may only be logged by pilots with a qualification to fly in IMC....), then you couldn't claim PIC IFR flight time credit.
Which leaves you needing another 25 hours of instrument instruction time to complete, not 15!
Simplest way at the moment:
1. Obtain a UK IR(R) - for which you will receive credit for all instrument flight time.
2. Use it to gain 15 hrs PIC under IFR.
3. Top up with whatever else you need to complete the CB IR.
If you later want to go into commercial flying, your CB IR exams wouldn't be credited. However, if you took the ATPL exams, they would cover the CB IR theoretical knowledge requirements.