Excessive memory usage

Hi, everyone!

I encounter a problem in my open world game, I built a large island with elements spread over the entire island (a village, a stadium, warehouses, an EasyRoads road, a factory etc.). The number of GameObject thus starts to be important on the scene.
When I make a build of the game, the memory consumption is very excessive (6Go used or more) and the number of FPS is very low (less than 20) so almost unplayable.

All my objects are well equipped with LOD and I built the occlusion culling. All objects are also in static.

Would you have solutions for a scene containing a large number of GameObject so that the memory consumption is much less important?

Thanks very much for your help!