Unluckily, you probably can't reduce it too much more, I'm seeing about 43 MB of low shared memory usage, along with a few hundred MB's of high shared memory.
Helps to have VIRTUALADDRESSLIMIT as high as you can without instability.
Truth is that upstream doesn't care too much about memory as they don't care about 32 bit systems much anymore. There likely are ways to lower the webengines memory usage, need Dmitiry to get back to working on it and it sounds like he has a lot on his plate with us being low priority.
As an aside, github just got worse with Dooble-Qt5, no longer displaying the code and such. It's depressing.