So have you had the dishwasher pulled out and checked the bottom base to see if theres water in there?
When you say the bottom base are we talking about inside the dishwasher itself under the filters or have had the dishwasher out and removed the side panel and checked in the base were all the workings are?
Ok E15 error code means water has leaked into the base and has activated the flood switch in there.
Not sure how you checked the base but the best thing to do is lie the the dishwasher on its back as i assume you still have it pulled out.
And while its on its back check to see if water comes out from the bottom.
Stand it up right and retry it and see how it goes from there.
But if that doesnt cure it then you need to remove the left hand side panel and there in the bottom right corner you will see a red plastic rod. Lift this up and down a few times as this is the flood switch and it can get stuck.
Then retry it and see how it goes. But if after all that its still the same flashing E15 then the control board is the fault. But to be honest this is very rare as its nearly always down to water leaking into the base of the flood switch is stuck. So try them and see how it goes from there.
Just wondering how you got on with the dishwasher as the question is still open?
Do you still need help on this? If not then if you could rate the answer then that will close the question.