http://muswell-hill.com/business-websites/wm2/faults/error-codes-hotpoint.html
http://www.qer.biz/find/FindModelBrandHotHy.html
http://www.qer.biz/lists/laundrymodels-hotpoint_other.html
This may be relevant as well, since it is toi do with the fill sensor. IN this case it was not detecting maciuchine empty, but a blocked pipe could equally stop the pressure sensor detecting machine full:
http://www.justanswer.com/uk-appliance/67c5b-hotpoint-ultima-1200-stopped-error-code-e15-check-drain.html
Anon, February 2015