Thank you for the advice. There really was a problem with the culling of the objects. As I found out the camera of the editor viewport doesn’t work the same as the in-game camera. It doesn’t cull the objects that are hidden by other objects. So you can look into the wall and have 5 fps because it loads all the sections and objects of the level that are situated behind that wall. Better set the distance of the far plane view, this is the setting right near the fov in the editor viewport.
What is also interesting is that editor is very sensitive to additional windows and tabs opened and it can cut fps really radically. It is wise to minimize them.
As for the different video cards I am beginning to think that there is a big dependency on the amount of memory or something like that. Anyway it is still a kind of riddle as to how the card gets loaded
Anyway, a big thanks for your help guys 