To what extent does lowering fermatation temperature of red wine from 25 degrees C to 15 degrees C effect how long it takes to ferment?

My homebrew kit says it takes 7-10 days at 25-30 C. My house averages 15 C and its already taken 16 days and airlock activity has not showed any significant signs of slowing down. Its difficult for me to tell as it speeds up and slows down a lot. The fermentor is against the radiator to keep warm, but when I'm at work I turn off the heating to save money, and the outside temperature can be as low as 2. Well it is only March I suppose. The house never gets that cold though. Its a fairly warm house which doesn't lose heat quick. Im just hoping for some finish product sometime before Christmas lol