Hmm, Devon is sort of remote.
There used to be an app on Google play called speedboost by an author called MC STEALTH (although I haven't been able to find it lately) it connected to you to a closer mast.
Are you sure there's a nothing going on on in the background that could warrant a heavy download? Maps, Facebook, YouTube streams?
Also, try a different speed test site. Not like that will fix anything.
I did notice when I was a data user the speeds were poor, and have seen plenty of people on here who are less than happy with the data service.