How much RAM does system use really?

I have 3x 2GB ram which makes it a total of 6GB. But my system uses about 1.5GB... is it normal? Or is it just me?
Update: I have 3x 2GB ram which makes it a total of 6GB. But my system uses about a whopping 1.5GB... is it normal? Or is it just me? Most system will use about 15% only right?
11 answers 11