org-self-insert-cluster-for-undo

org-self-insert-cluster-for-undo is a variable defined in `org.el'.
Its value is

nil

Documentation:
Non-nil means cluster self-insert commands for undo when possible.
If this is set, then, like in the Emacs command loop, 20 consecutive
characters will be undone together.
This is configurable, because there is some impact on typing performance.

You can customize this variable.