I understand, personally I have not encountered this bug, but Arma sometimes reserves this kind of bug, unfortunately.
Unfortunately by changing the value of the bank, the same bug you encounter will cause the player to lose what he banked. Who will be replaced by the $ 15,000.
Edit :
You can always test this solution:
In the file ... /server/players/setupPlayerDB.sqf
(line 47)
["BankMoney", _player getVariable ["bmoney", 0]],
Change the value to:
["BankMoney", _player getVariable ["bmoney", 15000]],
But I do not guarantee the result.
Regards,
Only Paranoids survive ...