13 Units for me!
i'm doing 13 units now for the HSC and I'm fine!
I also have a friend at skool, and he is doing 15units and going really well! And no he is not some walking brain! he he
Good Luck with what you do, just make sure your happy with what you've got!
If your happy with the subjects and enjoy them, you'll be fine - also as long as you keep up with the work!
If you don't like them, you may have some probs! And stress may build up!
Have you tried speaking to your school subject coordinator or counsellor, they may be able to give you some ideas and support?!