This plug-in seems useful – not tried out: details
“This Plugin facilitates users to reduce the size of all textures in the model / selection. The SketchUp users can utilize this plugin at the time of sharing a large file having so many textures rapidly. This can be useful if you want to quickly share a file that is too big because of extensive textures. It can also be beneficial if any user applies photos directly from the camera and intends to batch-downsample to an optimum resolution.”