This might help also.
Thanks a lot Marc and Zber very helpful.
9 million per SubTool is way overkill if you are going to merge to a 2k or 4k map. But to answer your questions, yes you can have all the subtools as a single polygroups by clicking Ctrl+W while all the subtools are visible. Once that’s done you can use UV Master to make a new UV map, and then make your texture map as a single map.