Cura is designed to have two separate processes. On the one hand, we have the user interface and on the other hand, the Cura engine. Since the engine runs separately it won't have an effect on the user interface speed. Unfortunately, it still results in a constant updating user interface which can be distracting.
There is an option in the preferences panel to disable the automatic slicing.
Go to Tools > Preferences or Cura > Preferences, depending on the operating system.
The slice status bar in the bottom right corner of the screen will stop slicing automatically, and state 'Ready to slice'. The button in the bottom right now changed into a 'prepare' button. Every time you make a change this button has to be pressed for the engine to start slicing.