This is not strictly speaking a programming issue, but definitely something quite annoying.
On my Windows 10 on my DELL OptiPlex, opening an excel file used to take about 30 seconds! It didn't matter if the file was on a local or network folder!
The issue was, in my case, related to the Audio Driver. Yes! An issue with Excel was related to the Realtek Audio Driver!
Anyway, here is the Dell's post:
http://www.dell.com/support/article/de/de/debsdt1/sln306701/slow-performance-issues-in-excel-when-opening-saved-files?lang=en
Solution:
Find your Computer Version in http://www.dell.com/support/drivers/home and update your Audio Driver
