Honestly, surveyors will be fatigued by the 10th question if not before. The most we have asked in one sitting with success is 12 questions. It might be best to break up the survey into several follow-ups. As for the slowness; I don't see that being an issue.

Regarding the Qualtrics editor performance, make sure to break up your questions into blocks. Even if it doesn't make any difference on the respondent side, it will make it easier to work with in the editor.
Also note that, once you have added a certain number of items in a block (I don't know the exact number), Qualtrics adds a "Large block mode" option at the top of block, which you can toggle on or off. When on, it displays the question text but removes the graphic elements (condensing the choices into parentheses). But in my experience the interface starts to get pretty clumsy even before you reach this threshold of number of items in a block.