I've found quite the opposite...that 10.11 shuts down impressively quickly.
10.12 took upwards of a full minute to shut down during the 17 seconds I ran it.
That might depend on which apps you have open when you shut down. For me, shutdown is very quick except when I have Entourage 2008 open. Then, it takes about 20 seconds.
OS 10.15.3, iMac Retina 5K 27-inch, late 2014, 3.5 GHz Intel Core i5, 1 TB fusion drive, 16 GB RAM, Epson SureColor P600, Photoshop CC, Lightroom CC, MS Office 365