Please note that these terrains were generated from the ground up to be used as game-assets.

Snowy mountains made in Gaia, it's an awesome free tool, you should check it out if you ever need a landscape creation tool for nature scenes, The blend file contains the scene I used to create the thumbnail, all the embedded textures have 1k resolution, the no. of polygons mentioned in the technical details are of the individual subdivided planes being used for the height maps

The Meshes have clean topology (since, they are just subdivided planes) which allows them to be easily decimated or subdivided further.If you wish to use these in a scene, bear in mind that the meshes use displacement maps to form the shape of the terrain. You can adjust the parameters to give you higher performance in the rendered view in comparison to the viewport to be able to work efficiently without any straggle

Hope you have a lot of fun with this product :)