I do accounting with Excel but my office mates use LibreOffice. It takes them about 50 seconds to open my XLSX file with 70kb. If I save it as XLS the file gets bigger (170kb) but LO Calc opens it in 5 seconds. The file has 6 sheets, data in 350 rows and 30 columns. About 200 cells contain formulas.
Switch to Libre
Office or save as .xls
I only can emphasize what @karolus wrote above. Change to LibO and be happy!!! Many of my friends and collaborators did so; they are happy too.
Well what is your question?