DIAGNOSIS E:15 is a water fill error. The dishwasher didn't get the water it expected within a certain time. This is usually caused by a kinked inlet hose, clogged inlet screen, or low water pressure at the valve.
FIX 1) Turn off the power and water supply to the dishwasher. 2) Pull it out and inspect the thin, braided water inlet hose behind it. Make sure it isn't kinked or crushed. 3) Where the hose connects to the dishwasher's water inlet valve, there's a small cylindrical screen. Unscrew the hose (have a towel ready) and use needle-nose pliers to gently pull out that little screen. Rinse it clean of any sediment or debris. Reinstall everything, turn water and power back on, and try a cycle.
IF THAT DIDN'T WORK The water inlet valve itself might be failing and not opening properly, or your home's water pressure to that line is too low. You can test pressure at the sink nearby. A faulty valve needs replacement.
HEADS UP Always use the supplied Bosch inlet hose if possible. After clearing an E:15, you might need to reset the error. You can do this by holding the Start button for 3 seconds, or by turning the power off at the breaker for a minute.