Let me start off by saying that I wanted to create this topic to keep us up-to-date about 7.1.5 changes, plus people could discuss ideas/calculate specs as well.
So far, the frost dk build received the following buffs on 7.1.5 PTR
1) Breath of Sindragosa is getting a massive buff (it was increased 250% from 175%, now it will be 287% -- still subject to change !)
2) Hungering Rune Weapon Duration increased, additional 20 RP and runes from that.
3) Howling Blast DMG talent improved
4) Horn of Winter buffed.
5) Remorseless Winter Damage Stacking (15%) Buff
There is one nerf, which is scaling of Howling Blast with AP
Overall, it is looking really strong in PvP, but Blizzard is now removing the consistency spec out of the equation I believe.
I will try to include up-to-date info, please feel free to contribute. All the best !