I came across this while searching for comparisons of window managers and their bare minimum resource requirements. I was kind of surprised. I know some smaller distros have switched to OpenBox, which had the largest resident set size of the window managers listed — three-times that of jwm. I wasn’t too surprised, though, that wmii also had a larger rss than JWM because of my experience with the MyDSL extension for it; even though wmii uses less than half (8 versus 19) libraries of jwm, its rss and vsize are over twice that of jwm and size is 10-times of jwm.
How much memory does your window manager use? You can check yourself with the command ps -ao comm,size,rss,vsize.