My 2014 Tiguan's battery keeps draining after leaving the door or lights on for more than 15 minutes. I have checked the battery it's fine.what could be possible problem?

True or something could be left in such as a dome light, side light or something constantly on like a aftermarket radio?

If your battery drains that fast....You should see a rather large spark if you disconnect one terminal of battery for a moment....If you have an ammeter, connect it in series with the cable, start lifting fuses in fuse block until the heavy drain stops.......Use caution...If you feel this is too risky, then use an ohmmeter connected to the pos battery cable after its 'removed" from the battery...lift fuses until the ohms reading jumps up much higher...that will be the item [circuit ] causing it..