When drag drop textures to unity’s project folder, texture import process automatically occur, and it is very slow.
for below 1 hundred can be tolerable, but if few thousand textures, almost few days taken to just import.
How to turn off or shorten this process?
Unity have to import the textures to be able to use them.
You can put all files in the unity project folder and import them at once.
If you have a massive amount of textures , just close unity in the evening and put all texture in the project folder via The explorer / filer.
Then start unity and let them import overnight.
If you have the project on multiple workstation you may should use the "Team License is an add-on " to sync the one imported Textures between the workstations to save the importing time on the other machines.