According to the Wikipedia page for Ubuntu, Ubuntu ran GNOME only until version 10.10, which is when Unity was released.
However, according to Sysinfo, my computer has GNOME.
I have Ubuntu 15.04.
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Screenshot your desktop and we can tell you what version at-a-glance you're running.
If you're running plain old standard Ubuntu 15.04, then you'll have some GNOME components, but you're using Unity.
If you're running Ubuntu GNOME 15.04, then you're using the GNOME environment. This is a specialized variant, though, which has GNOME as the primary desktop environment and not Unity. (It's a different installer ISO as well)