I am not a teacher, so I can't speak to the extra work outside of normal business hours. When I first went back to school, I was still working full time. I only had 10 credits, and I was pretty busy. I am not working now, and I can easily handle 15-18 credits.
The most important things to remember:
1. Good GPA > fast completion
2. Many universities may not offer night classes for pre-reqs. If the one(s) near you don't, head to the CC. Make sure you are aware of the advantages/ disadvantages of community colleges.