It really depends.
- If you have discrete graphics you may get away with it. If you have integrated graphics then probably not. Since the integrated graphics will eat up 2GB.
- If you turn off all other programs and clean up your startup programs. So, that only the minimum number of programs start with Windows that are necessary for your programs to run. Which you should do anyways to clean up your computer.
- If you are clear on both counts above. You are probably safe. Games rarely use as much RAM as the box states. They play it safe. Assuming people will leave some programs open, have a computer loaded with unnecessary startup items and be using integrated graphics.
Also you can check whatever the game is and 6GB RAM. There's...