Just for reference, I've been a phone/dsl tech for 30+ years and there are a number of things that effect DSL speed but loop length is the biggest. (aside from actual line fault issues)..
A DSLAM is antiquated at best and looses some speed right off, better systems use a single point dial tone source with the DSL in it and ideally that system uses a Broadcom chipset, proven to work best. It also needs to be a DSL2+ system or better a VDSL system but here's some distance info for you.. Expect 20% variation in this based on crappy house wiring, how much if any 22awg is between you and the CO (most will be 24awg all the way, not as good) but assuming 24awg, excellent house wiring and no copper faults..
0-1km from CO, 22meg to 26meg
1-2km from CO, 20+meg
2-3km from CO, 15-20meg
3-4km from CO, 10-15meg
4-5km from CO, 6-12meg
5-6km from CO, 1-6meg
6km+ from CO, total crap shoot if you even connect, SNR will be sub 5db and service unreliable uniess provisioned for a pretty low speed, IE 1meg.
With a decent amount of 22awg cable in your route, add 1km or more to any of those IE 4-5km from CO but 3/4 of the loop is 22awg, 15meg is easy.
Keep in mind loop length can be shorter than the drive distance (IE goes through a right of way) or much longer (IE goes to a x box then back to you))
I've been doing this for years and for a company that allows us to do what we need to do to meet numbers on par with that. DSL is a horrible technology by todays standards but can be reasonably fast if everything is excellent (and that includes no cracked insulators or poor transformers on the Hydro lines too)
Hope that helps! Odds are they're on an old ADSL-H cards, they are prone to noise etc but even on one of those at 2km 8meg is doable. We sell 5M, 10M and 20M but we won't install the 20M over 3.5km nor the 10M over 5KM.