Importing from an iPhone 6 will hang if another user on the same Mac has Lightroom active as well. So if more than a single instance of LR is active on the same Mac, import from iPhone will hang. Import from a HD folder does work, however.
I'm having the same problem. LR 2015.6, Mac El Capitan. It started after I updated LR to 2015.6. For a while it was a bit of a lottery as to whether LR could find the photos on the iPhone 6S -- I often finished up with the endlessly spinning wheel and had to force quit LR. Now it mostly just endlessly says it's looking for images, with no result. The outcome is at the moment I can't import photos from my iPhone at all. Never had this problem before. Is Adobe looking at this one?