HT discretion on the amount of training required prior to undertaking the EASA ATPL exams. Really depends on whether or not you feel confident and capable of passing without additional tutoring or not.
Some of the subjects should be second nature such as IFR/VFR Comms, HPL, etc. But some of them can be quite tricky - MET and Air Law for example. If you don't have the time to do face-to-face revision, check out the online stuff from Bristol Ground School and start hitting the question bank to see where you are capable of succeeding and where you need additional help.