I don't have a 6+ but it seems like it would be similar to running with one of those big gluten-free chocolate chip cookies they sell at Starbucks. Eventually you get used to it.
Are there shorts with a zipper that can fit an iPhone 6+? Something like a zipper that will prevent the iPhone 6+ from moving when running. I think this would be the best approach if I want to run with my iPhone 6+. If there is something like this please share. Thanks!