Look. I really hate to be harsh here, but this is terrible advice.
Yes you’ll lose weight because eating only 1500 calories a day is definitional malnutrition. Any “diet” which claims that is healthy is very literally encouraging people to develop eating disorders. You absurdly absolutely can’t do it by “eating anything you want.”
Unless you are doing this under strict super vision from a dietician and your doctor, for a specific medical reason, it is extremely dangerous and more likely to cause other problems with your overall health in the long run. You will almost certainly not get the nutrie ta your body needs to function correctly if you are not carefully monitoring what you are eating with professional help. You’re also significantly more likely to end up with an eating disorder. These diets are extremely harmful, I hate seeing them literally everywhere.
You may have seen results in losing weight in such a “diet” because you were very literally starving your body of the calories it needs to function. That just isn’t a healthy way to lose weight.
If your doctor is telling you that you are in good health and the only reason you want to lose weight is cosmetic, don’t do it. Unless it is directly impacting your health and your doctor is recommending it and supervising it, forcing yourself to eat significantly less than what you need to function is not safe.