There are several possible causes for very slow model loading, other than a slow internet connection.
1. File size
When the file size is large, long downloading time is inevitable.
If the texture file being used has a resolution of 2048 * 2048 pixel, the file size could around 10 MB.
If you are not so picky about the resolution, you can downsize the file by 1/16 with texture resolution of 515 pixels per side.
2.Number of materials
Lesser the number of materials, faster the rendering of the model.
You can reduce the number of materials by applying single material on multiple meshes during 3D model creation.