Both good points, thank you. There are several more years, but I hadn't realized until I did some research that the 4% rate was relatively low (it's a floor rate, think it is prime + 0.5).
The $15k is our only liquid personal cash right now, though we're in a good place to build that up quickly. I think I'll take a middle road, and pay off 80-90% of the debt...this keeps the line open, minimizes interest payments, and keeps a small (but growing!) nest egg of cash.
Thanks!!