E15 means water has leaked into the base and its activated the anti flood switch.
The best way to clear the base is to pull the dishwasher out and tip it backwards so you will need a towel for this part. Let all the water drain out from the base and this will then let the anti flood switch reset.
This way clears the base a lot easyer then removing panel at the bottom as with it having a soild plastic base it makes it hard to do it this way as you cannot clear all the water.
Once its clear retry it and if it happens again then theres a water leak in there which you need to find.
Remove the left and right hand side panels as this will give you access to the under side of the appliance. Set it going and watch it while it does a wash and try and see were the leak is coming from.
Check the wash motor on the right hand side as these do like to leak in there.
But doing reset wont clear the error code if the anti flood switch is activated.
If you need anymore info just get back to me.
Usually to get it out you need to remove the wooden plynth at the bottom.
Then open the door and look at the very top in each corner and there should be a screw holding the dishwasher to the underside of the work top. Remove this and lower the feet and it should pull out from there. That's if its installed correctly.