Dear Diana,
The changes are going to be substantial: first and foremost reading and use of English are merged into one part, each exercise is going to be shorter, but also the students will have less time. In CAE for example the part in which they had to come up with one word matching 3 sentences is out.
Listening is virtually unchanged.
Another big difference is connected to writing: in CAE P1 there is a compulsory essay to write, in P2 they still have a choice of a letter, report, review or proposal.
In the speaking test the main difference is that in the collaborative part instead of pictures to discuss, the candidates will have verbal prompts (pictures were sometimes confusing).
As usual, the choice whether to buy or not is yours. I guess if you are thinking of teaching this level not just this single time, you īll need to invest in these books... For the time being you can always download the free handbook for teachers with one complete test and mp3 track.
Hope that helps :-)
http://www.cambridgeenglish.org/images/cambridge-english-advanced-handbook-2015.pdf