I'm no electrical engineer so I am just going by what the phone company technician told me and that was that on their copper lines, 18,000 feet was the max they could provide DSL. A friend up the road is at that maximum (he's last one on the line with DSL and his service was very sketchy to the point he finally cancelled it.)
We had a problem even getting reliable phone service here. For a few months, if it rained our phone wouldn't ring and it became a party line where we could hear other people's conversations. This is a rural area with inadequate and aged infrastructure and an unwillingness of ATT to invest into any improvements after they acquired us from Southern Bell. We cancelled our phone line and just use cell phones now. Saves about $400 a year.