The players have 12 minutes to answer 50 questions. While I am not diminishing the people who took this test, I feel that ESPN is missing the point for giving you 5 minutes to answer 15 questions.
The sample test has 15 questions @ and at 4.1667 seconds (50/12) per question you would have to give yourself only ~ 1 minute to answer that quiz in a similar test environment.
It is tricky but with little or no time pressure you are allowed to think. Remember, it is a quiz used to evaluate QBs, players who have to think and make decisions quickly in pressure situations.
Edit: So lets say you give yourself 1 minute to take the test, and answer 4, you would need to do (4/15)*50 to get your "Official Wonderlic Score" (13).