I have a mac mini (Late 2012) 2,3 GHz Intel Core i7, 8 Go 1333 MHz DDR3 with bluetooth keyboard and trackpad.
Since I upgraded to El Capitan many tasks are incredibly slower than before. For example, the boot time before I get the login prompt is 80 seconds.
Then, once I entered the password it takes 90 additional seconds before the Finder is stable (without the colored wheel popping on and off)
Then when I click on Safari, it takes Safari 23 seconds before I can actually type in the address bar. Note that after that even if I quit Safari, it will restart in a second. So I'm measuring here the first start after boot.
Total: That's more than 3 minutes before I crawl the web which takes me back to the first imac with macOS 9 ages. (Joke: Was it a preliminary information that macOS days are coming back?)
Seriously, I wonder if it's related to my machine or to El Capitan. Could you answer how long are these timings in your configuration so that I can compare?