No. It won't kill you, but it will kill your social life and hobbies.
12 hours was real do-able when I went through occupational therapy school, worked 32-35 hours at a real flexible job, and raised three kids without welfare or child support. Some semesters were 15 hours and I got through them. One semester ended up being 18 credit hours with 6 weeks of a weekend statistics class. I also moved the family the weekend before finals, and ended up needing IVs to finish the semester.
I did all my cooking on Saturdays for the week. Every "break" I got my research done for upcoming papers. Yeah, I lost weight, too.
Every time I weakened I remembered a friend asking, "So what will you do tomorrow if you don't go to class?" Didn't have a good answer. Also put a big sign on my wall in front of where I studied that just said, "Keep you eye on the prize." Meant something to me. Find what means something to you.
You can do it.