Each instance of the IDE appears to take around ~300 MB.
But I don't think this warning is dire enough as to how much memory it's going to actually consume. This is how much memory it ended up consuming in the quiz result view (on Firefox).
It completely froze my 4GB RAM potato when I did the quiz. I recently upgraded to 16GB and even then it struggled (it started swapping even though I'm not running anything but the browser).
The article already warns that:
But I don't think this warning is dire enough as to how much memory it's going to actually consume. This is how much memory it ended up consuming in the quiz result view (on Firefox).