Hello, thanks for reporting the bug! Yeah we've recently had reports regarding load times being really bad for some people, we're currently looking into it, but if you don't mind can you upload a campaign save and your output.log file? That might show us what's causing the issue.
EDIT: For a workaround, you can try deleting your Xenonauts 2 folder on Documents/MyGames/Xenonauts-2 and see if it helps.