I assume you're talking about 15 KB/s (as in Kilo BYTES)... just a nitpicky point: if you write the "b" in lower case (ie: Kbps), it means kiloBITS.
Anyway... enough of that!
What is your DSL line supposed to be running at? 15 KB is pretty slow (translates to about 120 Kb/s). Sounds like your provider has oversubscribed on the POP you connect to.
The slowest ADSL service I've seen around my area is 640 Kb/s download speed.