I got same problem. I'v got 16 GB ram and GF t 1080 4GB. And game seems to use only 4 GB of ram max according to task menager... this is the problem i think. and i do not see anywhere in files option to change ram usage... i would fix it myself .
Strange . I turned off manually antialiasing (0). aint a pretty thing but work smooth now. Really waiting for quick fix.