I am in a very similar situation to yourself. Flu jab 2 years ago triggered the PMR virtually overnight. After 18 months had very bad side effects from methotrexate. PMR is self-limiting and will eventually go any for nearly everybody, but the issue is that no one knows how long in will last for any individual. Doctors do tend to be very optimistic when they quote 2 years or less to their patients.

If the steroids have been useless so far have you investigated what dosage is needed in more detail. It could be that you need a higher dose. That - like the time PMR can last - can be a very individual thing. Sometimes 15 mg daily isn't high enough initially and no progress can be made at that dose. Soem people like myself readily needed to start out at a much higher dose to crush the inflammation before any relief could be had and it was only after that that tapering could be considered. But if steroids - even at a higher than usual dose - don't work then the doctor would normally considered whether the PMR diagnosis was accurate.