Since updating to El Capitan .6 on various Macs, we are having issues with general slowness/sluggish performance. One of the main things is that copying and pasting files/folders takes an age! Even small text files takes much longer than it should.
It happens when copying both locally and over the network. I've attached a photo that shows an example of a 38KB file being copied over the network, which was stuck at the '38 KB of 38 KB - Estimating time remaining...' screen for 5mins.