Low performance issue due to culling. How to turn it off?

Hi, I am developing a car game and the performance in the highway set up is just terrible, even compared with other scenes such as a city, that is way more detailed.

I checked up both scenes with the profiler, and culling was DEVOURING cpu time in that scene, something that isn't happening in the city. Even if I disable the geometry of the 'terrain' (I use quotes because it is not Unity terrain), the culling keeps using a ridiculous amount of CPU. This terrain is huge and made of huge portions of geometry, but I have discarded this to be the probrem by itself because disabling it barely improves frame rate.

I have deleted the baked culling info for this scene and used the profiler again, but the culling was still eating CPU :(

Is there any way to turn off culling completely? Will bakíng it with a really big cell size make it better? And dividing the geometry in smaller blocks?

Thank you for your attention.