Photoshop are consuming 13GB of RAm to create Gradient

Can you recheck your document size. You would not be the first to have created a 1920 x 1080 pixel document that turned out on rechecking to be 1920 x 1080 inches

Dave

Photoshop needs 3 to 5 times the size of each open document in RAM. So depending on the size (and layers, bit depth play a role) is large enough, this isn't necessarily unusual. 

What is the height, width and resolution of your image?  Large images consume more resources than small ones.

Restart your computer to reset scratch disk and RAM.

Ensure your computer is robust enough to handle the workload.  

- https://helpx.adobe.com/creative-cloud/system-requirements.html

Pay particular attention to Photoshop's new GPU requirements. See links below.
- https://helpx.adobe.com/photoshop/system-requirements.html
- https://helpx.adobe.com/photoshop/kb/photoshop-cc-gpu-card-faq.html