Decimate modifier and textures not looking good

I’m using decimate modifier from ~4M to 20k, it fails and stops at 67k. Do you have any ideas how to avoid that? And also what does happen here actually? UV-maps are screwed? Should I think of doing texture re-baking?

4M is far to much for such a simple building. There is something wrong from the start i guess.
It is made in blender or imported?

Textures are messed up by decimating geometry, at a point it goes totally broken. Use the unsubdivide option if you havent, it is not so worse.

Thank you! I see that the trees take lots of the mesh density, so it’s not even. Unsubdivide would be great if it’d be buildings. Here is I’m afraid that the goad is 20k, so I should find way