The successful pass of the 14 subjects of the ATPL (A) Theory is the first step. And it is obligatory for everybody, regardless of the applicant's flight experience.
A total of 1.500 hours or more will just allow the applicant to take the exams without registering in an ATO and without a Theoretical Training Course Completion Certificate.
When it comes to flight training, portos8 is absolutely right. EASA regulations leave the flight training at the discretion of the HOT or the CFI of any approved ATO.
However the Skill test for IR training needs to be conducted in an EASA member state and that is why most flight schools propose 15 hours of IR training just for the applicant to become familiar with the country's airspace.
Things are different when it comes to the endorsement of an ICAO Type rating on an EASA license. The 14 subjects of the ATPL(A) Theory are still a prerequisite, but in order for the Type Rating to be endorsed on the license, the applicant needs to have logged 500 hours on type.
As far as I know, the prices of a Conversion Course in Greece range from 8.000 to 10.500 Euros.