I created an artificially blown up ics file available from https://bugs.kde.org/attachment.cgi?id=14413&action=view This file has 1.2MB and more than 3900 events. Having it loaded and doing "New Task" does not take 1 second, neither does deleting. My computer is 5 years old (PIV). Please tell me if this is slow for you. If you do not answer, I will have to close the bug again because I cannot observe the problem.