Set Keyboard Repeat Delay and Rate
From Gentoo Wiki
If you are working with Vim for example, navigating through text can be much faster with a higher autorepeat rate.
You can use the xset command to set 400 milliseconds delay and 100 repeat rate.
xset r rate 400 100
Open System Settings and navigate to Input Devices module, then Keyboard. Set Delay and Rate to your preferred values.