no, it'll use as much as it needs. how much of your ram is the game itself using. Windows will cache up to about 80% leaving only a bit free for new and uncached programs. it is very good at it, don't mess.
When its not freezing like right now it is 654 and within a minute it has rose to 752, now 10 mins later it is at 1.5GB and still rising, game crashed instead of lagging to hell.