You take your AS level exams in June 2015, and your A2 level exams in June 2016, you haven't been affected by the "end of two years" changes.
So for maths, you will take C1, C2 and [M1/S1/D1] in June 2015.
The workload is manageable. I took Maths, Physics, Biology and Media and whilst they do like to pile on homework (because there is so much content, especially in Biology), it's nothing a decent work ethic can't handle. However, come exam time, maths will have three exams, so you will have to do nine exams, not eight like most people you know, so be sure to plan your time well about six weeks before your first exam.