The way that the IR(R) / IMCR credit has been described is somewhat misleading.
For the CB IR, the applicant needs to have a total of 40 hrs of instrument flight time (not 'IFR' flight time). Of this, 25 hrs has to be instrument flight training, with up to 15 hrs credit for previous training (e.g. for the IR(R) / IMCR) - which does NOT need to have been at an ATO! A further 15 hrs credit for instrument flight time (not 'IFR' flight time) gained as PIC for IR(R) / IMCR / EIR holders is also available - hence the 30 hrs total.
In other words 15hr IR(R) training + 15hr IR(R) PIC = 30 hrs; a further 10 hrs of instrument flight training is needed which MUST be at an ATO.