I don't think it's anywhere near $15 a barrel. The lifting cost is more than that. According to Moody's the break-even point is about $42 a barrel industry wide. I don't think Permian is that far off.
Some analysts peg the ballpark break-even of pulling oil out of the West Texas ground at $35 to $40, making it one of more cost-effective energy plays in the United States
I think Ace is pretty close here.
There are about 50 bazillion variables involved with profitability in the O&G sector and every company has their own number. It all depends on the geology, lease acquisition costs and 50 bazillion (minus 2) other things. Some companies are getting really good at saving money, but shale drilling is just mega expensive to begin with. Continental Resources is probably the king at well engineering, with Devon and Chesapeake doing some good work too.