The Universe is far older than 15 billion years.
Everyone must also take in to affect that after the Big Bang, chaos was turned into order. Creation of spacious gases which give birth to stars and all that amazing stuff that I won't go into detail. Our Earth and rather other planets within solar systems and galaxies,didn't form in 7 days or anything like that. According to religion, there is a timeline to all that, but it's not true. Don't get into a religious debate here either, I know what's up with my religion and the cosmos. But anyways, within this "explosion", everything on the basis of everything in the universe came from this thing. The things that make up you and me and Lavos originated from the "bang". In a sense, we are ALL the same, hypothetically speaking.