A well taught IMC will reduce the stress on the IR, and will enable you to complete the course in minimum hours.
A badly taught IMC will mean you'll have to unlearn it all for the IR.
Make sure the IMC is taught by someone who has an IR and who has real-life IMC experience. PPL instructors don't need IRs to teach an IMC, so you could be taught by someone who has never actually flown in IMC!