Ask HN: I'm Looking for Interview Question about Java Around Web Development

Hello, currently we are hiring for a Java Developer (middle skill) and looking for "good" interview questsions, however I'm actually a little bit clueless, about what are good questions. We don't want the task last longer than maximum of 15 minutes and it should be around Java and Web development.

We will probably start with Fizz Buzz, but after that we wan't to be a little bit more specific to our problems instead of asking algorhitmic questions. I tought about creating a small guestbook with java (framework doesn't matter). would that be a reasonable choice?