If Excel is closed and I open the Excel application, it opens quickly. If I then use Excel to open a Workbook, it also opens quickly.

HOWEVER:

If Excel is closed and I double-click a workbook to open it, it opens EXTREMELY slowly (like, take a potty break).

I've tried unloading all of my add-ins, no change.

What gives, and how can I fix it? And BTW, thanks so much for even reading this, much more for any light you can shed on the issue.