You’re assuming influxdb stores it’s data in a single file. It might have lots of small files, it does whatever it needs to do in it’s container.
You said influxdb is only 80mb so why is it relevant? You had to increase the size of the vm by 16gb and now are having to do it again. The 80mb addon isn’t the problem.
Do you have full backups? Full backups tell you the size of every piece in them you can partially restore. If one of the things in there is huge I would start there. If the backups aren’t big then i would look at your logs. And when I say logs here I don’t mean that file in /config. I mean your real logs, the system journal, see this guide for how to access it:
How big is that? Logs are something that can grow without bound if you have issues that you aren’t paying attention to.