You dont necesarily have to buy the newest if you have 15 plus. That model will be good and perfectly functional for couple more years. So instead of complaining how you cant spend 2k$ to get the best new big iphone, you could simply save for a year and buy one next year, if - as you say - you like your current plus so much. And your family member could receive a different one, or maybe you could buy them a new (17)..
Of course to each their own, I just find it funny, there is so many options yet people always find a way to want something more or different. It's probably the worst technology feat...