Have you downloaded the practice tests and tried them? You can get them here:
http://www.tda.gov.uk/skillstests.aspx
I'm not doing a PPGCE but work in one of the test centres. I tried the online testsand passed all three so they cant be that hard! (I haven't been to Uni).
I find it differs from person to person - some come in and pass all 3 tests in one session, others I see so often I am on first name terms with them! It's not even the same test that they fail, they all have problems with different ones.