When to upgrade from T15 to SoO gear? Ret

[Zard 0]

I'm having trouble when to upgrade out of 2/4pc T15 into the SoO gear from normal to normal versions. I look at the logs and all the top rets still use their 4pc heroic versions, but I am not sure if it should be the same for normal to normal upgrades.The only thing is, for me, is understanding when to opt out of the T15 4pc/2pc to 553 gear when I only have normal versions. 

 

http://us.battle.net/wow/en/character/eredar/Zardarious/simple

 

Here is the current gear I am thinking of switching to, I still have all 5 pieces of the T15 normal versions. Its just I'm having trouble understanding that T15 4pc > all of the stats gained from upgrading 522ilvl (530) to 553ilvl (561) (567 warforged). Until I have 4pcT16 at once.

And if the 4pc really is that strong, could you care to explain for me so I can fully understand why it is stronger than gaining the stats from the upgrades?