Sky ADSL speed check was right, BT and others wrong?

When i joined Sky a few years back they said they estimated i could get 4.5mb down because of a long line.
The speed i got was very close to the estimate.
Doing a check with BT and other providers then and even now estimate i will only receive up to 1.5mbs.
Do sky do something different?

The BT database has probably just become more cautious over the years to avoid complaints. You might see a difference due to a new connection and DLM kicking in but it may be better or worse than what you currently see - although likely not a big swing either way.

Also a very small chance that BT is selling only ADSL on exchange, but Sky has LLU so ADSL2+ available.

Its a very small chance though.