Updating large amounts of data

My situation is that I have a reporting program that takes a snapshot of the inventory levels for each part every evening and uploads it as an .xls file to a folder on our network. It includes quantities as well as $ on hand. This happen for three locaions, and so for each day there are three new files added with a combined row count of 12,086.  We've been collecting data since Feb 2023 and as the amount of records grow the amount of time to update is gettting outragiously long.  
I'm looking for some ideas to reduce the refresh time.