What "gimmick" are you suggesting? If you are referring to use of iPad chargers, this is no gimmick. That's all I have used for last three years. It does not hear up my iPhone 6s Plus unless I am at same time playing some graphic intense game.
Using the iPad charger is completely safe and approved by Apple. If your phone is hot and you are not actively playing a game I suggest you have a runaway app using your cell radios or are in midst of massive download like I experience for about 15 minutes when I first set up this new phone.