This can be done in a variety of ways, although the easiest method is to create a custom event. From the WSR menu, select "Events", then "Custom Event", and create a 15 minute Endurance race on any track, against very easy AI drivers. Just race your best and you should be able to start lapping opponents within 5-10 minutes, gaining the achievement immediately in-game. Once you get the achievement, feel free to back out.
You can also do this online with a friend in any race event. Just have your friend drive in circles at the start line until you lap them for the achievement to unlock.