I believe the 16" got a significant bump up in its discrete graphics card, and I'm pretty sure it kicks on whenever you plug in a second monitor, no matter what

I believe the 16" got a significant bump up in its discrete graphics card, and I'm pretty sure it kicks on whenever you plug in a second monitor, no matter what else you're doing. That card has been by far the greatest driver of heat/fan speed in my usage; more than the CPU.