2015 and 2012 iMac Displays

I was wondering if it is possible to connect my 2015 21.5" iMac and my 2012 21.5" iMac together, so the 2012 could be an external display for the 2015? I want to connect them so I can drag my mouse from one screen to the other without having to connect two separate mice and keyboards. I tried connecting them via the ethernet ports on the back, as well with a USB cord, but neither worked.

I was wondering if I should try to connect them both via their Thunderbolt 2 ports? Or if connecting them to each other to use one as an external display was not possible due to Apple's restrictions with graphic display/what devices can act as external displays. Any information would be helpful. Thank you.