When working with different 3D file types, it's important to understand your options for texturing. Some textures live in a texture map (as a separate PNG or JPG), and others live in the vertices of your 3D model. It's important to understand these differences and be able to manipulate the texture separately from your 3D mesh. This would allow you to output a smaller file, with a low polygon count but a high resolution texture. Watch this video to learn how to do this: