Force `imortrange()’ to update data

I’m using the importrange() formula inside of Google Sheets to import a bunch of data from multiple spreadsheets into one sheet. On this one sheet I’m using circa 20 importrange() formula’s each importing circa 250 cells.

The problem is if I change any of the data in the original source sheets the import sheet takes hours to update. Any idea why this would be and what I can do to force an update