Update: A lot more data has been gathered, please scroll down to see - the original parse consisted of a tiny amount by comparison.
Big preface/disclaimer: I recognize the element of RNG in this game. When a set bonus is released that introduces further RNG, there will be scenarios to a variety of extremes.
I had heard from a few people who realid me for frost mage stuffs that the 4pc of Tier 15, (6% FoF increase change off Frostbolt) was underwhelming. One person suggested that it might just not even be active.
So, I decided to do a 10 minute test with the following parameters:
No buttons pressed other than frostbolt, ice lance, and invocation (can't go oom).
When a FoF proc is generated, ice lance is hit immediately so that all FoF procs are tracked.
These are the results.
My major concern here is the # of frostbolts cast versus the # of FoF generated.
With a statistical time frame of 10 minutes (600 sec), I calculate the following:
Haste gain from the ilvl boost of 522 tier is 10 more frostbolts: 3.01% more frostbolts
% of FoF procs in Tier 15: 11.34%
% of FoF procs in Tier 14 (half 517, half 496, all I have sorry): 13.77%
Difference in yield: -2.43% FoF procs using T15
Difference in yield considering potential set bonus: -8.43% FoF procs using T15
So, referring back to my disclaimer, and taking RNG into consideration, it still really appears this set bonus is not active. I encourage others to run tests as well. If I find the time after raid tonight I'll try to run even more 10 minute tests to prove that this is not a case of RNG.
Sidenote: 2pc of 517 tier will really last a while, that bonus is substantial!