As you continue to fast your metabolism will slow down and the rate of weight loss will slow down considerably. Your present rate of 1.5 pounds a day is pretty average for the first week or so. You will probably see a loss of a half pound or less a day as your body slows down, this is simply how fasting works. Many people find that their rate of weight loss is faster when they fast one or two days a week and eat a healthy, nutrient dense but low calorie diet the rest of the time. One of the biggest issues that long term fasters face is a rapid weight gain once the fast is over and eating returns. A low calorie diet must be maintained for weeks or months while the metabolism returns to normal. I don't know if this is what you mean by a plateau, but it is part of the physiology of fasting.