When troubleshooting, one of the things you can easily try is Safe Boot (Safe Mode Startup)
- Hold Shift Key and press power button
- Take your hand off from the Shift Key when login window appears
- Enter user name and password
- Hold Shift Key again then hit [Enter] to proceed login process
- Take your hand off from the Shift Key when you see the Desktop background image
Shift Key from the power up up til login window disables third party system extension(s), and Shift Key after login will disable third party user level extension(s). If the performance improves then you can blame something troublesome is caused by 3rd party software you have installed.