Reasons about the excel file operat slowly...

Excel file slowly, reason:
1. Hiden Object (press F5, to check object, which once not use for, just delete, may be user draw some line or some objet but don't have color on it, and foget it, using for long, they copy it become many object, and make heavy)
2. Name not use for. (press Ctrl + F3 to see, if not use for just delete)
3. Many format (every font size, every color, ... that is 1 format, if in excel file so many of format need to make it down)
4. Picture didn't compress
5. Column and Row don't using but have color and format (Press Ctrl + End, to check which cell is final cell)
If excel file have many sheets, you need to make 1 sheet become 1 file
And check that every file, see which file heavy
If heavy, just compare with that 5 reason and fix