I have had this problem on my Silverado Midnight Edition built early 2015 and bought new on July 2015 a month ago.
I went for an oil change at 67000KM and they found my radiator was leaking. At first Dealer asked me to pay for a full repair and then I found the recall on this Forum (Thank you). The Dealer/GM Canada told me the recall was for 2014 models only and they did not want to repair it under the 'Powertrain Warranty'. They asked me to pay 50% of the repair as the initial 3 years warranty was expired. I do not understand why GM does not fully honor this warranty (Powertrain) on early 2015 models that does have the same problem as 2014 models. The GM representative told me GM was doing modifications on their truck every year, but they did repair my truck with the same parts as of the recall. I can also tell the leak was minimal and was probably there for at least a year. Although I am a Chevy fan since I am young, I lost my confidence in GM products and might go elsewhere on my next purchase.
So I would like to advise every Canadian early 2015 owners to ask the dealer to check the Radiator before the initial 3 years warranty expires.