As a year 12 further mathematician who is doing the whole A Level in year 12, I can safely say that A2 is quite a lot harder than AS. I've just got my mock back for the whole of the AS, and I got 92%. But in the A2 mock I only got 76% (and that was on the first 5 chapters). It was mainly just due to not having practised the content for long enough, but it can get quite messy sometimes.
Trust me, when you get into year 2 content, especially integration, you will find AS piss easy in comparison. It makes it look so easy honestly. Then again A2 isn't that hard once you know what you're doing.