Understanding Intel iris graphic card spec for mac mini
The Intel Iris graphic chipset uses shared memory meaning it allocates up to 1.5GB (not 1.5Ghz which is frequency or more commonly known as speed) of RAM from the system to be used as VRAM.

So, If you have a Mac mini with 8GB of RAM, you really have a Mac mini with 6.5GB of usable RAM because 1.5GB was allocated to video.

From Apple's website:  Integrated Video on Intel-based Macs


  Apple computers using Intel Iris Graphics as the primary GPU dynamically allocate up to 1.5 GB of system memory. 


You were correct in your presumption - it's not a powerful graphics card built onto the CPU.

You should check with the vendor of your software to see if it has a requirement of 1GB of dedicated video memory (meaning it's built into the card and doesn't share with the system) or not.