Regarding: KOrganizer 5.1.3 on Kubuntu 16.04

I'd like to set a default reminder time in KOrganizer. I tried to do so unter "Settings" / "Configure KOrganizer..." / "Time and Date" / "Default Values" / "Default reminder time" and set it to a value different from the default value. When I restart KOrganizer und restart my system, the value is still what I set it to but it doesn't have any effect: Whenever I create a new To-Do, the reminder time is set to the default of 15 minutes and I have to change the value by hand. Deleting my calender and creating a new calender doesn't change this behaviour.

So my question is: How can I effectively set a default reminder time in KOrganizer which is different from the default value of 15 minute?

Thanks in advance.