Now that the 15 has USB-C, I’d like to see if it correctly supports USB-PD. Is there any way to tell the charging speed when you plug in your phone to charge? With my Android it would say “Charging Slowly”, “Charging” and “Charging Rapidly” or I could use some apps. I haven’t found anything with my iPhone though.
I'm not aware of a way to do that with software. You can buy one of those USB meters for about $20, they tell you how much power is moving through. Something like this (though I'm not sure if this exact model supports USB-PD):