I doubt your parasitic current draw has anything to do with ground or chaffed wiring.
More than likely a problem with an electronic component that is not shutting off, radio, GM5 module, keyfob antenna, BMW Assist or something like that.
Suggest you actually measure the current draw after 16 minutes the car should go into sleep mode and the current draw should drop.
If you have a way to automatically log the current draw, this would be good to see what the current draw does over time.
I would expect that the sleep or standby current draw should be approximatle7 40-90 mA as the max. Even 90 mA is probably on the high side, but this is just guess as I have not actually measured any of my BMW's yet.
The other thing is have you checked the battery out completely, what is the battery reserve capacity and what type of battery are you using?