The ATPL exams are very much more difficult than the ppl exams, the main difficulty I found was the huge amount of information that has to be memorised & all at the same time. There were many days when it seemed that the light at the end of the tunnel was permanently switched off.
It took me 15 months to pass my exams (5 hrs a day study)
Good luck - If you are determined you'll get there in the end