I compared them in the store today (I have 16" M1 MBP and looking to switch to a smaller/lighter device)
The display is nice, scaled resolution almost the same (probably corresponding to 15" vs 16" difference), brightness without hacks looks the same, sharpness difference is visible only when you look at the display from a few centimeters, from normal viewing distance zero chance to see that 16" is sharper.
What you will notice immediately is obviously 60 vs 120hz... everything is so much smoother on the 16", which is funny since when using a standard 4k 60hz screen (with mouse) I don't really care about it, but when I scroll a webpage with a trackpad I noticed the difference immediately haha (probably comparing to the speed of my finger moving on the trackpad...
Despite all this I will most probably order it, the size/weight difference is very noticeable. Just grabbing the laptop and running from meeting room to meeting room would be soo much comfortable with the 15" air (only thing I will surely be missing is the HDMI, back to carrying the bloody dongle again...)
Thanks. Speaking of 60 vs 120hz, do most people notice the difference?