S, thanks, here some moe info. I doubt it will help. I find that everyone who complains on forums about not enough info, when I give more info, they never have the solution anyway:
It's a white mac laptop about three years old in the living room. It's sharing the excel file originating from the other room.
other devices? ...? packet 8 phone in the router.
No need to test, it's much slower dealing with the excel file on the mac in the other room. You can feel the sluggishness with saving, changing text.