I've just checked out past paper mark schemes and the 15 mark answers - there's no way we had enough time to answer to the depth they needed us to answer in for Unit 1 and 2.
Some 15 mark answers are slightly over half a page in length and that's bullet point format and there's no way I can think, plan, and then write that much in prose in 15 mins!
I can't remember Unit 3 and 4's 15 markers, but my teacher thought the AS paper was harder than usual so I'm surprised that grade boundaries have gone up as a lot of people seem to have struggled (many in trying to decipher what the question was actually asking, especially on the constitution!).
Also, what happened to sticky post for Unit 1 and 2? There were some fantastic resources/discussions there on topics/answers.