I had the unfotunate idea of moving out of iPhotos to the new Photos app. Later, I decided to migrate to LR6. But there is no way I could migrate my library in keeping albums and organization I have done in iPhotos/Photos... Did they arrive at any solution for that?
I don't have a Mac and can only Google for answers to your question, but the last item in the following article looks reasonably simple and involved using the iPhotos import plug-in that I think is built into LR but changing the location from where to import from. I have no idea if it keeps your albums intact or is just going to give you an large folder of all your photos, perhaps grouped by year or some other coarse division.