Did someone else some heroic PTR testing as frost? It was pretty terrible to be honest. The council fight was a real mess, had some badluck with FoF Proc and Tortos was just terrible. After 30 min I switched to Arcane on each boss, and the difference was huge!!! Way more DPS (approx 40% - 45%) and arcane was way more mobile (Arcane Explosion is priceless to keep stacks up) than frost (I know, no instants like Ice Lance or BF-FFB, but anyways).
The Frostbolt debuff is still an issue, more than before to be honest. Because of the higher procchance from Frostbolt, you switch target with already 1 stack FoF (because you need to do focus dmg) and with the first frostbolt, you gain a second stack FoF and you have to clear one with 10% less dmg, you cast another frostbolt and gain another stack FoF and you have to clear with 5% less dmg.
Frost feels a little bit like arcane (stationary), but without it´s damage output.
By the way, I´ve played with the new T15 4p and my FoF Uptime (according to Skada) was only 15.9%. That´s way to low.
Conclusion: Frost is still way behind other classes and the other mage specs (damage wise). Playingstyle is, compared to cataclysm, unsatisfying resp. insufficient. Don´t see any serious progress raider playing frost, who have to fight for his spot (if things stays unchangend).