How many calories should I be burning

Kgantshom, Each KG of weight you need to lose requires you to burn 7700 calories more than you eat. Your daily burn without doing any exercise is probably about 1700 calories if you're lightly active. The lowest safe calorie intake is 1200 a day. Less than that and your body thinks it's being starved and it will lower your body functions to burn fewer calories.

Your goal is 15kg in 18 weeks. So each week you need to lose 15KG/18weeks or 0.83KG. This would require you to burn 0.83*7700 or about 6400 calories a week less than you eat. Dropping to the minimum of 1200 calories will mean that in a week through diet alone drop 3500 calories (1700-1200 = 500 * 7 days = 3500), meaning that you still need to burn 2900 calories each week through exercise to hit your goal. Moderate exercise burns (in women) about 8 calories a minute. HEAVY exercise is about 10 a minute. So assuming that you do 90% moderate and 10% heavy exercise you need to do about 360 minutes of exercise each week, or about an hour a day 6 days a week, with one rest day. Examples of moderate exercise are running at 8kph. Heavy would be aerobics with weights. MFP will help you estimate your calorie burn for a typical exercise.

Depending on how out of shape you are right now this may not be a realistic goal. When I started my quest to lose weight I could not do an hour of moderate exercise, walking at 5kph was about it, and I had to go longer to get my necessary calorie burn. After I could do 6.5 km with hills in 80 minutes I moved to the gym.

BTW your goal is at about the maximum recommended weight loss target. This is a very hard goal, and while achievable, it will be very difficult. Keep that in mind if you lose at a slower rate.