You could try if lowering the resolution helps
Thanks for the suggestion.
The screen resolution is 1366x768, so not very high to begin with, and lowering it makes everything rather blurry. Not sure how much it helps performance wise.
I found that running the x86 version, even though it is a x86_64 machine, helps immensely since then the game requires less memory and the system doesn't swap.
I managed to peek at htop while running the x86_64 version and that showed 1.3 GB in swap. Given that the OS and DE take about 400 MB of memory that means a lot of game data is in swap as well, being written to and read from a really slow HDD all the time.
Given that I estimate the x86_64 version requires at least 5 GB of memory.
One issue I experience is that the game crashes after a couple of minutes. I tried with the Nvidia as well as onboard Intel drivers (I think, unless I did something wrong). Is this a known issue?