It's not difficult, as the HSK level 6 isn't very difficult for Chinese native speakers.....although there are usually a few things you need to watch out for during the rest as it has been made by Chinese people. They broadcast it through some kind of radio in order to prevent cheating. So the sund quality is usually really bad, at best. Try and get a seat near wherever the speakers of the classroom which the test will be held in. This will give you an edge.
Another tip is to always try and read the a-d answers in advance that way you will be able know what to listen for. Good luck on your test!