My home internet is 15/2. I have tried to watch HD via the 922, and it really does not work well. It cuts in and out all the time. SD works OK (watching an HD program using SD sling). 2Mbit up is just not fast enough. I suspect given how close it comes to working that the minimum is somewhere between 2 and 3 Mbit for HD. But, given the ins and outs of the internet with congestion, they probably quote a lot more just to be sure it is fairly reliable.
The minimum for SD sling is probably pretty low.
The minimum for SD sling is probably pretty low.