Going from 2015 to 2024 you probably will need to download a trial version of something in the middle, like 2019. (Or even 2018, then 2021.)
Obviously make a few copies of the QB Company Folder (not compressed) as well as having QB Backups (compressed). Then go ahead and try to do an update straight to 2024, but if it doesn't work don't panic. Just talk to them about progressively updating.
