I'm not very hopeful here because I've found where my rural client's cabinet is (~2km away) and the expected speeds of VDSL2 at that distance. The 15Mbps they are getting through speedtest seems very much as expected. But if somebody with far more knowledge than me could cast their eye over the statistics and make any comments, I'd be eternally grateful:

https://www.dropbox.com/s/pqodqdy5q0plyhi/VDSL2%20statistics.png?dl=0

Thanks, Rob.

PS. The link itself seems pretty stable. When I first connected it up, speedtest was getting around 13.5Mbps but it's gone up by about 1Mbps since.