My new Mac runs slower

I replaced my old 27-inch iMac (Late 2012) with a late 2015 model of the same size. Its performance seems inferior to my old iMac, although that had a Fusion Drive, unlike the new one. It often shows the spinning beach ball, and prior to shutting down it

Odd display effects at shutdown can be an early sign of graphics card problems. Disconnect all peripherals apart from keyboard, mouse, and network connection, and hook up your keyboard and mouse to USB ports. Shut the iMac down, wait a few seconds, and hold D as you start up the Mac again to run Apple Diagnostics. If its tests record an error, contact Apple Support or take the Mac to a Genius Bar.

Check the Mac thoroughly for old software, particularly extensions and persistent services which might have migrated from your old iMac. You shouldn’t be seeing the beach ball so often; Activity Monitor and EtreCheck (Free, etrecheck.com) can provide clues. Another trick is to download and install the latest macOS Sierra Combo update from Apple’s site ( apple.co/2k2hNJV) over the top of your existing installation. After that, you may need to force your Mac to check for later security data: in System Preferences, click the App Store icon, disable “Automatically check for updates,” then enable it again.