I, too, have been using Mobil1 15w50, changed every 6,000 miles. Now have over 70,000 miles. No issues, other than a recent "dreaded rear seal leak".
No evidence has been presented that the type of oil used makes any difference ref: the leak.
It's also alleged that our bikes ship with synth, though I can't confirm that.
That said, one of "Benson's Laws" is that "Oil Is Oil". I don't think there's an oil out there (within reason) that would really hurt our bikes. K-Bike engines can run 200,000 miles without major wear. There is no major problem with K-Bikes going down with lubrication-related failures at any mileage regardless of oil used.
BTW, my Honda Element shipped with synth and the first oil change is called for at 10,000 miles. I'm going to stick with the recommendations (I have about 8,000 miles on the original- I assume they know what they're doing.)