Most obese people, strangely enough, don't eat that much at all. They drop their calories so low that their metabolism slows. Then they get tired of eating rabbit food. When they go back to their 'regular' eating habits, they're now burning fewer calories at rest. So, they can fatten up with 1500 calories or so, especially if it's loaded with fat and carbs they aren't burning.
MAYBE in some people, lower metabolic rate or whatever accounts for some weight gain (as in a couple of pounds, MAYBE). However, nobody ever got obese eating 1500 calories a day. It defies the laws of the physics (namely "the conservation of energy law"). If you consume more energy than you expend, you store it as weight. Keep doing this consistently, day after day, year after year and you will become obese.
There is nothing more frustrating than an obese person who in public eats only healthy foods claiming they "cannot lose weight" or its their metabolism. You just know that at some point, in their own privacy, they are gorging themselves.