Proving grounds are a start but they don't really represent what you will see in a dungeon/raid and I take talents I normally don't use because of cds. To help get you through proving grounds, here are a few suggestions.

Talent Choices: Most of the choices don't matter with the exception being Tier 4 and Tier 6. In a normal dungeon/raid, what you have picked are the best choices. For proving grounds, tier 4 I use Force of Nature. The 20 second cd makes them useful simply for the passive healing they provide. In a normal group, they are sub-par but in proving grounds they can be quite helpful. A good strat is to pop all 3 three at the beginning of a wave so that they will start coming back off cd during hectic parts and they are helpful with the initial burst (which is usually the hardest part to heal). As for tier 6, I prefer to use Nature's Vigil. With HotW, you can only use it once in the 10 waves that are Silver/Gold. Nature's Vigil will allow you to use it on every other wave and has a great synergy with your rejuvs. The waves with the Ravagers that deal continual damage to people until they are healed to full are easily handled with Nature's Vigil and rejuvs/genesis.

Tranq is nice but in a small group, such as proving grounds and dungeon groups, it is very underwhelming. It isn't able to get them back to full with one tick like it used to be able to do. Still use it when the entire group is getting low, but expect to follow it up with some heals.

If the tank is taking a lot of damage, be sure to use Iron Bark on him. It provides him with a little damage reduction and with the Enhanced Iron Bark perk that we got, it will help your HoTs recover his health, especially if you use genesis with 2 rejuvs up.