Thank you for posting in answers.slingbox.com! That's a great question! An upload speed of 1.5 is sufficient for SD streaming or even HD streaming with any model that is older than a Slingbox 350 or 500.
Below is a link to an article from our support site that provides the bandwidth requirement for streaming with the all Slingbox Models:
Have a great day!
The Sling Moderation Team