Decrease memory usage of terrain?

I sculpted the terrain of an island, not grass or trees, just the shape of the island.

I noticed a 20K increase of memory usage after that. Is it possible to downgrade, voxelate, decimate the polygon count of the entire terrain? I really dont mind less detail for a surface used just for walking, running.

Your thoughts?

Common case is you would want it to work well if driving too. I wonder if values are less when you import a simple heightmap.

You lost me there, can you clarify what you meant by driving?

Maybe smaller terrain, with doubled or tripled scale.

Probably previous experience, with some vehicles driving too fast and going through the terrain, I think it happened when RR first started.