Last week I bought a new 2015 iMac 21.5” with retina display and new graphic card. Three days later I returned it to the store. Set it up on desk and computer took 3 tries to boot up. When I went into System Preferences, After I changed the screen resolution, after which Display icon disappeared. Then the beach ball from hell started up. Not a good sign!!! I downloaded some of my info from my 4 year old iMac and the new iMac ran very slow. I called Apple Care twice. Once, the person on the other end took over my computer and rebooted the hard drive. Didn’t fix anything. Called Apple Care again and was told to upgrade from 10.11 to the 10.11.1 fix. Was told that would fix everything. Didn’t fix anything. I'm very disappointed, I desperately need a new computer. So, should I buy a new 21.5" iMac now or wait for a few months.