Even with everything off I get a draft through the air vents on my 2015 EX. Is this normal?

 

If the selecter is set to fresh air, and not set to recirculate, then yes, this would be considered normal when the car is moving....

 

If fresh is selected, absolutely.
The body vents in the rear cause air to be pulled through the car while moving.

 

Yes, and I like it that way... No fan needed. In my ST, it closes the vent when the fan is off. So the only way to have fresh air is to have the fan on low which is a waste. So I do prefer the Honda fresh air method because you can slide the vent to recirc to keep the air out when you drive through a dust cloud easily enough.

 

I think the air flow is rather weak with fresh air and no fan, I was a bit disappointed that I had to engage the fan to get a little breeze going.

 

Yeah, there is a little air circulation with no fan, but, being a fresh air fiend, I always run the fan.

 

Airflow increases substantially with the sunroof open without much additional noise compared to lowering the windows.

 

That's true! Amazing how much of a difference the sunroof makes.