Why is the web page taking a long time to load?

Is this a good question to ask during interviews? I do feel like it tests the problem-solving skills of candidates. Can he/she tell me all the possible causes? Can the break the issue down to its components? Can they identify the different items that can cause problems?

Further, if they do say there is something wrong with the server code ( which is normally their top answer) , I can dig deeper into their ideas on improving the efficiency of the code.