Do you have any antivirus software running that integrates with Outlook to
scan incoming/outgoing messages? If so, try disabling it and see if that
does the trick.
Also as neo mentioned DSL accounts are typically asymmetrical. If your DSL
is 150K per second, I'm guessing you're referring to KB (kilobytes) and not
Kb (kilobits). Note the difference in the case of the "b" in those.
Having said that, is this referring to your download or your upload speed?
150KB/sec would be about a 1.5mbit DSL connection, and if you're upping at
10-12KB/sec then that would indicate a 128kbit upload. A typical low-end
DSL package in many areas could be a 1.5mbit download/128kbit upload
connection (particularly if you're far away from the central office), so if
that's the type of connection you have then the behavior you're experiencing
is typical.
If however you are saying that you can upload to a website (like uploading
an attachment to Hotmail/Gmail for example) and are getting speeds of
150KB/sec, then I'd refer to my inital suggestion about the antivirus.
Outlook does not inherently have any controls for bandwidth limiting of
outbound connections. If something is slowing it down, it's something
external to Outlook.
Joe