All organisms produce more offspring than can survive in the world.
After about 500 years, there should only be about 16 thousand elephants, not 15 million. The basic problem, however, remains, a few elephants can produce lots of elephants. Now let us suppose that all elephants grew up to a ripe old age of about 90 years. These elephants have a total volume of cubic meters, or times the volume of the earth. If these elephants were formed into a spherical herd, it would have a radius of meters, or a diameter of light years.