I know the general principle of UI design, that giving people two ways to do one task is confusing and actually slows them down. But in this specific case, I think the two ways of changing a question category are sufficiently different that they are not confusing, and they are both useful in different circumstances, so I think we should keep them both.
I am sure that it should not take more than a few hundred milliseconds to get the list of all the categories.
No one has said whether they have a lot of publised course categories. With a lot of published categores, question_category_coursename() function will querying the database once for each published category. That is really bad. It would be better to use a join to get the coursename.
Are you able to try the attached patch on your system, and see whether it makes a difference? If so, I'll check it in. The patch is against 1.6.2+. I hope it makes sense in the 1.5.x context. Thanks.
Quiz
Slow question edition
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