It depends on each individual - I coped easily with Maths, Further Maths and Economics and 7 (occasionally 14) hours a week straight through A2, including my exam period. During AS til Xmas A2 I was only doing 10 hours though. It depends when your hours are. When I was doing 10, it was 5 on both Fri and Sat nights, which was at the sacrifice of my social life. Working 7 though was on a Saturday, which was pretty good as it left Sunday for work. Do what suits you, and if you're struggling then you need to cut back the hours if possible. Working 40 during the holidays now that your 16 is possible.