Is doing 8 hours of ballet training enough to help me gain a career in dance?

Anything less than 15 hours a week year round of technique classes ( 20 for a ballet career) is considered recreational training. At age 15 if you are not training full time in a professional level school ( affiliate feeder school to a professional ballet company in most if not all cases) you can forget ballet as a career. For other dance genres for a performance career you still need to more than double your current training especially if some of it is assistant teaching which does nothing for your own training..

For a career as a recreational dance teacher you are still running short but as there are no real requirements for that, anyone with even little or poor training can call themselves a dance teacher. Hopefully you don't want to be that kind of dance teacher. There are university programs in schools like OKCU ( American Dance Teacher) that have special training and degrees for dance teachers. They teach dance pedagogy and kinesiology so you won't injure your students by pushing them too far or incorrectly. They also teach the business side along with your traditional dance classes. To ready yourself for this kind of school as auditions are required, look to up your training to at least 12 hours a week. Good luck.

Edit: If you are not in the USA it is very likely your country might have a similar type of program.

EDIT: I'm 15 by the way, I didn't state my age before sorry