I have one of the new Early 2015 MacBook Pro's 13".
I'm trying to daisy-chain two Dell U2515H displays using MST over DisplayPort, but I'm just getting the same image duplicated on each screen.
I've seen online that other people have got this working, albeit with other MST-supporting machines - the 13" MBP was added to that support doc after it's recent release, the pre 2015 version wasn't supported...