Q: Using 2 imacs.. one as a monitor?

Hello. I have a 2011 27inch Imac and a 2015 21inch Imac. is there anyway I can use the 21inch Imac as the main computer and have the 27 inch as a dual monitor with the 21 inch? The 21inch is newer and more powerful thats all, and it would save me buying a new display for the 21inch.

Any help would be appreciated.