This IS important, because it doesn't matter what worked for you in other games ... Although here is the same engine, but the architecture is own ... I know the project U4 (2x2 wall, which at START in MENU uses 8 GB of RAM -_-) ... If you don't want to answer, you will get a similar answer ... You are one of hundreds who have this problem ...
A memory leak is occurring. As an option ... maybe you don't have the Page File (8 + -GB) ... Perhaps you have enabled (along with the game) LOTS of applications (Browser, Torrent, etc.) = DISABLE ALL at the time the game starts -_- .. .. Probably Old archive files conflict = DELETE the OST_Game folder located in AppData \ Local ... you will not get any other advice.