Not being an expert on this but £14.99 per month sounds like the old price for NTL's lowest broadband offering, this has changed speeds over time (64k -> 128k -> 150k -> 300k -> 1Mb), people on that tier of service are now paying £17.99 per month though(i think).
Have you done any speed tests to confirm the speed that you are actually getting.
If not go to:
http://www.adslguide.org.uk/tools/speedtest.asp and see what it tells you.