I finally can play the game XD
The story is interesting and the graphics really good XD
Sadly it takes 6GB RAM when I played it. No wonder I can't played it the first time. :'
I don't know why it takes so much.
Maybe you can try partially rendering the 3D, so it will only render objects that shown on camera. I think you can also try to change it to rendering videos instead. So the video switched every time the scene changed. I think it will decrease the memory usage.