German high school system

I will be relocating to the Koln area in Germany with my son who at the time of relocation, will be 15. He will have finished grade 9 in Ontario and I want him to continue his studies in Gymnasium as it is the only high school which leads to university entrance I have heard, and it is the only type of school which goes beyond grade 10. Does anyone have experience with the school system and the integration of 15 yrs olds in the German school system and its success rate. Thanks.