9. The Disk Permissions repair fix
This isn’t exactly a El Capitan slow specific performance fix but it is good to run anyways, as this remedy can profoundly increase your Mac’s performance or just do nothing. Since it doesn’t do any harm, it doesn’t hurt to try.
To perform disk permissions repair, Restart your Mac -> Press the Option key as you restart -> Select Disc Utility -> Select OS X partition (or partition where you installed El Capitan) -> Choose fix disc permissions -> Restart your Mac.
If you do see a performance boost, it will be quite significant after a disk permissions repair run.
You can alternately run repair disk permissions without restarting your Mac as well. To do that, Press Command + Space-> Spotlight will open up -> Type Disk Utility -> Select OS X Partition -> Verify Disk Permissions -> Repair Disk Permissions
On a side note, your Mac would have automatically run disk permissions when you installed El Capitan, as Macs are programmed to run disk permissions repair every time OS X is updated. But again, running disk permissions repair at any given time doesn’t hurt and can only help.