That means that basically without crosstalk you could expect around 10Mbps.
With crosstalk, which is likely, speeds of 7.9 to 2.5Mbps.
Crosstalk usually hits at once, in my experience, so chances are 15 was without and 7.5 is with. Hopefully it'll stay around that speed.
Regarding 10 day training, no such thing on FTTC, that's all just CS lies. DLM runs all of the time on the line, it is kind of always in training, and will make adjustments to speed as and when it is required. This can work both ways, faster and slower.
What ADSL2+ speeds were you getting? It suggests 2.5 to 6.5 and often can be conservative?
ADSL2+ might give you a more stable speed, which does not vary often.
You mention BT laid the cabling for 200m down the drive and installed FTTC, did you never try bog standard broadband at this address?
Edited by ukhardy07 (Tue 02-Aug-16 14:30:21)