Losing so much weight in such a small amount of time is extremely unhealthy.
You are also very likely to gain back most of your weight, if you lose it so quickly. The rule with weight loss is that the longer you take to lose it, the longer it will stay off.
You can healthily lose half a kilo a week. So the most weight you will ever be able to lose in a month is about 3 kilograms. Losing 15 kilograms will take you about 4-5 months.
4-5 months is still a reasonable period of time to lose weight with. It is close enough into the future so that you don't get too inpatient or bored.
To lose weight the healthy way, you would have to reduce your calorie intake and exercise at least 4 times a week. And as I said, the longer you take to lose it, the longer it will stay off. So be sure to follow the healthy way to lose weight quickly and healthily.