I'm confused about Mac Mini's Iris Graphics

Hi. I just bought a new Mac Mini that has 8GB of RAM. It's still in the box because I'm not sure I made the right choice in buying it.

The reason I'm not sure if it was the right choice is I have some questions about the Intel Iris Graphics, which the Mini uses.

I read that Intel Iris Graphics uses 1.5GB of system RAM. Does that mean that the Mini really only has 6.5GB of RAM for general usage? Or am I confused?