I used to run a 2014 15 inch MBP in the office hooked up to two QHD monitors with the lid closed and I was apparently using a 65-watt charger from a 13-inch MBP. This worked fine as I guess the power draw from using the laptop was below 65 watts so that the laptop charged while in use. I have a 2015 15 inch MBP with AMD and it's using the Discrete Graphics (it needs to to support 2xQHD + internal) and I noticed the charge percentage dropping. So the 2015 + AMD uses more than 65 Watts. I plugged the 85 Watt charger in and it's rising again. Just a funny observation. It is very nice having the discrete graphics but it looks like it definitely uses a non-trivial amount of power.