best way i can describe bandwith on a normal connection is it act much like a seesaw
if your DL and UL are idle and your just sitting there then it will be level and your testing should come back fine.
If your getting better download speed ie 15.2-15.5 then your upload will suffer and vice versa now this is not the standard way of thinking but its the easiest and most undertood method for explaining the way bandwith works in most cases for services like cable and verizon's fios.
Hope that helps on explaining if it didnt oh well i tried and im vored so BLAH! LOL
but yea ur speed DL wise looks fine try re-testing a few times at different times and if it doesn't improve then try those cablenut settings unfortunately they can garantee 2Mbps on UP TO 2Mbps
Any more questions or just wanna know more lemme know i'm happpy to help.