Yes, 2015 is revised internally. Connecting rods and bearings. Thus the Theta II connecting rod bearing recall is not applicable to 2015 models. Everything bolted to the outside of the 2015 engines are the same, intake and exhaust manifolds etc. Metal shavings are the result of the affected engines' flawed assembly, not the cause. It has been hypothesized among factory training center instructors and several Kia Master Techs (myself included), the problem is that selective size connecting rod bearings are used in these engines and the wrong size (thickness) were selected at assembly. I've torn down dozens of these engines after failure, and all of the failures are due to excessive connecting rod clearance. Hope this info helps.
As far as oil selection, our dealership has used Valvoline Full Synthetic in both 5w-20 and 5w-30 for quite some time now to service all Kia and Mitsubishi cars. I personally use this in my 2015 Optima 2.4 lease, with a K&N HP-1004 oil filter and in my 2003 Mercury Marauder with a Ford Racing Performance Parts FL820S filter. This oil carries Dexos1 Gen2 approval for what it's worth.
On another note, when Theta engines are replaced under the SC147 connecting rod recall, Kia mandates the use of Mobil conventional 5W-30 as the break in oil, in both the 2.0 Turbo and the 2.4. They keep track of this by sending it to us in 55 gallon drums and warranty admin requires it to be charged to the repair order when the engine connecting rod inspection or engine replacement is completed. So Kia likes and/or requires Mobil conventional 5w-30 to be in there at least one time. Kia does not require our bulk oil to meet any specs besides API current spec, but our service manager is an ex General Motors service advisor and prefers to carry Dexos approved oil in bulk, for which I do not blame him. Typically the cars that come to us with either a locked up engine or a connecting rod hammering have NOT been serviced exclusively by our dealership and either have no oil change sticker in the window, or a Jiffy Lube, Wal-Mart or Firestone sticker, and some aftermarket version of the downsized PH6607 equivalent oil filter. (Smaller Nissan Filter that aftermarket TLE places use interchangeably with the proper, larger PH9688 equivalent). Probably because it's cheaper. So I would venture a guess that most of the engines replaced are also mistreated to some degree.
Sorry for the very wordy answer, but in conclusion I would, and do in fact use Valvoline Full Synthetic 5w-20 in mine and my customers' cars.