Hi
sorry for the late reply.
When I wanted to do my conversion, the LBA simply told me to find a flight school and come up with a conversion plan and submit it to them. Based on that plan, they would also give me the approval and the OK to go ahead. You also need a verification of your license by this authority.
The 14 written exams are a different story. From what I heard, the German Database is very different and involved, including questions that require you to explain your answers.
Like you mentioned, doing your training in Germany is way more expensive than say, Poland, Greece etc.
Best of luck