Talking from a point of view as a ground instructor, don't count on it. I have taught people with full FAA ATPL, all appreciated the classroom tuition. Some were fine, going through the course without difficulty but no more easily than other students. Others would happily admit they were less well-prepared than holders of JAA PPLs for the groundschool. Can you not get to the UK, US, Spain or any of the other countries teaching groundschool in English?
Best of luck, it's a tough course very different from the FAA one, but it can be done with hard work and basic understanding of maths.
P.S. Agree about a 300-hour course from inexperienced instructors. The CAA-approved courses are a minimum of 650 hours, typically a little longer, and I sat the course in 2000 when it was all new, even here, and that made life tougher.