I create a form with horizontal tabs and text_format element.
It takes so long time cause I can see there are 10 POST XSS request by ckeditor in ~2.60sec(https://www.dionach.com/blog/ckeditor-drupal-module-cross-site-scripting). I don't know why 10 because I got 34 text _format. Maybye it's an issue of library, if it is have you got a link to post an issue somewhere plz.