Perhaps I over estimated. I know that my 15 Gb hotspot allocation only lasted a few weeks (days was perhaps too strong). I used two carriers to get 30 Gb. But one MacOS upgrade (on one computer) and the allocation is gone.

And then there is Zoom.

I think that it is difficult to estimate one's internet usage if you can go somewhere else when you need do to something big. If 15 Gb is your only allocation, for home and work, it doesn't last long.