At that distance from the exchange, there has to be a problem with the line, either the BT bit or within the house. Try removing the master socket faceplate, and plug the router into the socket revealled. That will eliminate all house wiring. If the speed is still so slow, you'll have to persuade Orange to take it up with BT (you can't report broadband faults directly to BT). They will resist, as they have to pay BT for the search/repairs (I believe).
Sony Xperia Z5 review: Hands-on with the phone which the Z3+ should have been