Has anyone had issues with major items like heat exchanger etc for a Bryant 383KVA060155 model--80% efficiency unit--ours is currently in its 15th year now. Can you share your experience on what kind of problems to expect & is it worth repairing or buying a new one?

Normally you can get 20 plus years out of a heat exchanger. It's not uncommon for a HX to fail at 15 years. Has yours gone bad?