You think the high volume of iPhone 6 sales has anything to do with this?
Doubtful that has much to do with it. Most people who have Android devices will not switch to iOs that easily. If anything, more people will make the move from iOs to Android due to open-source support & better overall experience with customization & ease-of-use through Google. As for the dip in devices moved by Samsung, a few factors should be considered:
1.) People not needing to upgrade: either fear of losing unlimited data, not time for them do so for those who are on tiered data plans, or no need to do so due to phones being practically future-proof (starting from Galaxy S5, Note 3, & beyond).
2.) Economy: Disposable income levels have fallen for 7 years running, weighing luxury vs. necessity.
3.) Availability & choice of devices: Market saturation, numerous devices with close specifications, different costs, additional driver forces freedom of choice.
4.) Limit of growth constant: Only so much Samsung can possibly gain from constant mathematical growth, bubble theory of economics, eventually it does stop. Volume of those who switched 12-18 mos. or more recent to Samsung, takes away from potential prospects. Market share takes a hit. Only thing Samsung will take from this with the overall reduction of smartphone profits (which they are still extremely profitable) are cash-flows. Use that monetary capital for investment, R&D, & untapped market research.