For most people, drinking that much water is not unhealthy. Your kidneys are designed to change the amount of urine they make to match the amount of fluids you take in. However, people with any heart disease, liver disease, or kidney disease can do themselves a lot more harm than good by doing that. If you drink too much water too quickly (such as 15 glasses in an hour or two), you may alter the electrolyte balance in your blood which can be very dangerous. This is very rare in people with normal organs. There is little if any risk that you will make your bladder burst.
I will say that drinking that much water is not the best method to lose weight. Losing weight requires that you alter your diet to include more fruits and vegetables (at least 50% of your calories), and implement an exercise program.
I suggest that you schedule an appointment with your primary care physician
. The two of you can discuss your weight and how best to start losing weight. Your doctor
may be able to recommend a dietary and exercise plan that you can try. In addition, he or she may be able to recommend you see a nutritionist
who can spend more time with you constructing a diet which will be helpful.