Thank you for writing.
I can confirm that RadRichTextBox
deletes text from RichTextBox
extremely slow. However, It seems that this is not related with the spell checking. I have added this as a bug report to our Public Issue Trucking System
. Feel free to add your vote for it here: http://www.telerik.com/support/pits.aspx#/public/winforms/13910
Unfortunately, due to the internal implementation of the control, I am not able to provide you with a valid work around.
I have updated your Telerik Points
for this request.
I hope that you find this information useful. Please excuse us for the introduced inconvenience.
All the best,
the Telerik team