What is this tropical houseplant? I've had it for 15 years in a small pot and it grows woody vines with with waxy leaves and never gets rootbound.
This is Hoya carnosa and it requires bright light for flowering. It's easy to propagate; I have 11 plants like this from 11 leaves of the original plant.
This looks like Evergreen Clematis. A wonderful evergreen vine suitable for zone 5 and up. 15 years? Clematis armandii. White flowers with an almost too strong scent! I could be very wrong about the ID. 15 YEARS?? Never gets rootbound? You are saying you've never transplanted this plant in 15 YEARS??
Let's see if others can more accurately ID first. Has this plant never flowered? Indoors with little sun this makes sense. Have you ever fertilized? Hoya could be a candidate by Bamboo.