Loud clank 15 minutes after i turn car off

Hello, the only noise I can even possibly imagine your vehicle making that long after being shut off is the contraction and cooling of hot exhaust components. They will cool at different rates, and as such, they contract at different rates too. This would make a tick noise perhaps, not a loud clank -- but it's a guess. Have someone near you at a repair shop have a listen - set it up to happen as it always does and park it in their presence. Use this link to find some shops near you that can help with your concern: www.repairpal.com/repair-shops