On the Bosch dishwasher if error code 15 is observed it may be due to the w ater fill level exceeding the overflow limit. This may be due to a malfunct ion in the Bosch part # 752738 or generic part # 9000727504 it is called th e Inverter Control Board. This part is located under the right side of the dishwasher. That would be your right side when you stand in front of the di shwasher. The dishwasher will need to be completely pulled-out in order to access this area.
Instead of simply having a float with a simple inexpensive micro switch (wh ich can be easily accessed from the front) control the water level like mos t dishwasher manufacturers Bosch has assigned it to this module to control the water fill level. It is probably controlled by a timer which controls a relay. My guess is that sometimes this relay gets stuck probably due to no t enough high temperature or simply cheap metal being used on the contact p oints of the relay which causes the relay contact points to stick together in the closed position. I will be doing a more extensive observation when I have more time to be sure.
I would like to take this opportunity to NOT thank Bosch for NOT letting me talk to their tech support and to have me figure all this out on my own.