Editing the mesh or the shader of an object that’s linked to many other objects appearing in the scene can be slow because software needs to update the appearance of all the other instanced objects.
A simple solution to this is to unlink the object you want to edit, perform the necessary editing, and then relink all the othe objects to the updated one.
It’s best to group the objects beforehand so it will be easy to select them for relinking.
To unlink the object for faster editing:
Select the object, Press U and choose ‘Object & Data’
To link multiple objects to one:
Select all the objects, and click the recently edited one to make sure it’s the active object.
Press Ctrl + L and choose ‘Object Data’.
If you didn’t group all the linked objects for easy selection,
A quick way to select all linked objects is to select one of them and press Shift + L to access the ‘Select Linked’ commands.