Welcome @shannaam, I've had two bouts of PMR. The first one lasted 3-1/2 years, the second one lasted 1-1/2 years. There was a small study done in 1985 and I'm not sure much has changed.

"The duration of therapy and outcome were examined in 76 patients with polymyalgia rheumatica without evidence of temporal arteritis at presentation. Seventy-five patients received corticosteroids, with a mean prednisone dosage of 22.8 mg per day initially. Duration of therapy was assessed using life-table methods. No significant difference could be ascertained between groups segregated on the basis of age, sex, or initial steroid dosage. The median duration of therapy was 37.3 months. It was estimated that 40 percent of patients will require therapy longer than four years. Corticosteroids were permanently discontinued in 31 patients after a mean of 23.7 months of therapy. The data support the concept of two patient populations--one with limited disease and another requiring long-term therapy. Relapses were frequent, occurring in 56 percent of patients. Evolution of arteritis during the course of therapy was infrequent, occurring in only one patient. Steroid-related adverse effects occurred in 22.7 percent of patients and were more common in females. The data suggest that, although corticosteroids may be discontinued in some patients with polymyalgia rheumatica, prolonged therapy is required in a significant number."
--- Polymyalgia rheumatica. Duration of therapy and long-term outcome: https://pubmed.ncbi.nlm.nih.gov/4036982/

There is another discussion that might be helpful for those struggling with tapering off of prednisone.
-- PMR Dosages and Managing Symptoms: https://connect.mayoclinic.org/discussion/pmr-dosages/

Have you tried making any lifestyle changes to help with your PMR?