I know it sucks, but I would find another set of models to achieve what you’re after.
I took a look at it in Max(The FBX as the OBJ has vertices issues), and it’s 1000+ meshes and 31 materials with some very weird geometry.
If I were you, I would recreate the planet(ocean, landscapes, biomes etc) using a sphere and some low-poly geometry. Then you can use all the “prop” models like planes, trees, bushes, houses etc etc. to fill out the environment. You can then use instances, merged meshes or Solid Particles to add the props. You can even use the original model to export position, rotation and scale of all meshes. This way you won’t have to recreate everything, you just have to load the models and instantiate/clone/particleShape and set position/rotation/scale it n times depending on your export.
Just my two cents. But you might be able to use the model, if performance isn’t your number one issue.