I'd replace it. When I bought the place I live, it came with a 5 year old heat pump. Now, about ten years later, it has had multiple service call visits, and its going to fail for good between the next second and 1-2 years from now. To boot, the brand that was installed changes its parts every so often, so even basic stuff like fuses are impossible to come by, even though they are just regular 4A fuses with two prongs soldered on them.
I say be proactive and when summer is here, go with a standard furnace and A/C combo. In my experience, 10-15 years is as good as it gets for heat pumps, so you are lucky so far.
Plus, most heat pumps, when it is really cold, just turn on a backup heat element, so it negates most of their touted efficiency.