Actually, don't worry about the 28k number... it's a hardcoded string that
shows up in the taskmanager UI because RAS can't figure out the speed of the
port - the reason is this:
You're looking at the speed of the "internal" or "RAS Server (dial-in)"
interface - this is not really connected to any specific media - the RAS
server could be processing 1200-baud modem calls or VPN calls over a gigabit
ethernet link (or both at the same time).
You should check perfmon counters or use netmon to measure actual
throughput. If you are running a dedicated VPN server, you can measure
traffic on your LAN interfaces and come up with an approximate throughput
number.
1.5Mbps is most likely a light load for your VPN server (depending on your
hardware, of course) and you should be able to process packets as fast as
your DSL connection can handle them.
So while it's probably really faster than 28k, the other posters are right -
to make it faster, get a faster internet link - it will be your limiting
factor. 28kB/s instead of 28kb/s sounds reasonable as a maximum for your
link.
On a side note - if you are running older hardware (below the minimum
recommended) and are pumping over 10Mbps you may want to turn off PPP
compression if task manager is indicating high CPU usage.