I have had a Dracaena Marginata for about 8 years, and it was doing fine until it started dying a few years ago, when I realized I had to change the pot as the plant seemed to big. I changed the pot within the last year, and it doesn't seem to be growing very much if at all. I've had it this long and it's size is nearly the same as when first bought. I've read that they can be 15 feet tall. Why isn't it growing? Any help greatly appreciated thanks.