I just tried to play Doom demo o playkey. Unfortunately, even with an actual 8mbps connection (I know that's not that fast compared to some other places), it's pretty much unplayable. I'm in SE Asia, so maybe geographically that's an area that has more ping?
I think the problem is location for you. I've read the website and their servers are mainly in Europe and Russia.
I expect them to be more distributed after the ICO, so this will nog longer be an issue, but for now, the latency will probably kill your gaming experience.
I also read that you do need a 10Mbps minimum connection to be able to play 720..