Hotspot is not the problem in itself — what you plug into it is.
What a laptop uses
Computers pull updates the moment they find a network. Budget 1–2 GB across a morning of work.
The habit that fixes it
Set the network as metered on Windows, or pause automatic updates on macOS.
syla: for several days of work, a 20 GB plan costs less than three 5 GB top-ups.