Maybe I'm biased or something. But with the release firmware, I remember the Wii U Menu didn't show up until every item has its icon loaded.But it doesn't feel like more titles slows down anything in the menu as far as I could ever tell. It's just the populating of all your titles that might take a minute. Everything else seems to load up just as quickly as a Wii U does with 10 titles.
In later updates, they improved this to the actual behavior where it loads the Wii U Menu, had all the icons loaded or not.