Drinking just water to lose weight can be dangerous. Trying to lose that much weight that fast can also be unhealthy. Proper diet and exercise is the best way to lose weight. Instead of water at least drink Gatorade, or other "sports drinks' that contain electrolytes and potassium. Try to limit your caloric intake to around 1200-1500 calories a day........... And Exercise.
Drinking water does help your metabolism but it doesn't actually cause you loose any noticeable weight. The only way it would do this is if you normally drink unhealthy drinks, like pop, and replace those drinks with water, then you will notice a difference. I drink lots of water. A lot more than most people and it hasn't resulted in me losing any weight.
Losing 15 lbs in two weeks is unhealthy. Avg weight loss should be 2-3 lbs week unless severely obese. At 162 lbs your not obese unless your really young or short. Eight glasses of water a day recommended regardless of weight.