1.5GB of RAM is a lot. You didn't argue against what I said, you proved it correct...
1.5 GB out of 6 GB? Not even. That's just with Skype/Steam/Chrome all open too.
Relative to 6 GB, 1.5 GB of usage is not alot.
With Chrome/Skype/Steam/WMP, it goes up to 1.5 GB. That leaves a nice healthy 4.5 GB for games and most of the time they don't even use up more than 2.5 GB.
Window's memory usage is relative to the amount of RAM you have installed. Windows will likely use something around 600-900 MB if you only have 4GB of RAM. My laptop has 2GB with Windows 7 x86 and it uses 800 MB.
If I were you OP I would just reinstall my copy of Windows and buy more RAM.