This trophy is easier than it sounds. The best chance to get this trophy is on Hard Challenge 4, which requires you to escape Voldemort's bad guys. Make sure you select this under the Online Challenges, so it counts toward your 15 required and compare with a friend.
Once the challenge starts, just run up the hill to the left, and follow the path. Don't worry about knocking anyone down, just run. Press X to sprint for a short time. You should be able to make it to the top, and in the middle of the ruins in about a minute. This will put you in the top 1000 on the leaderboard, and trophy will pop after.