If it is 15 years old it is doubtful that it is over watered. Most likely it needs to be trimmed back. They grow easily from cuttings, so you can easily root new ones. In a tropical climate they grow fast and are pretty tough. They start looking crappy over time. I cut them back severely and root the cuttings. New growth will come up from the trunk if it is still viable. They sometimes just fade away with old age.