For High school i lost 7 lbs. the day before a meet. But my coaches told me to eat every small meal and a granola bar at 10:30am and 3:00pm to keep your bodys metabolism going. but consider not eating or drinking anything the day before you could easily loose 3 or 4 lbs. Plus your 1.5 you would probably loose in your sleep. 5 lbs. is easily achievable. good luck