hard to say... it's an A-level so a lot. Most A-levels have a lot of content and much more than GCSE.
I can't really compare it to anything else. I have pretty in detail notes, and I have like almost 2 full decent sized notebooks and am in year 13.
I would say, if you have a pretty good memory, or if it makes sense, its not hard to learn and remember the stuff. For example, a big topic is research methods, about experiments and stuff, but this comes up in almost every other topic, and you often come across approaches in other topics too. So learning new content kind of helps reinforcing old content. And some parts of research methods is kinda obvious.
If you think you will be interested or enjoy it, I would recommend it - its easier to work hard at a subject you enjoy than one you don't.