Sorry for the long post but have 2 major questions!

So my LO is 4.5 months old and at a weight check appt a week after his 4 month check up, I was told that the baby should be nursing AT LEAST 10 minutes on EACH breast. I want to know if any of you mommies actually nurse that long? My LO mainly nurses one boob (about 10-15 min) each feeding and seems satisfied. I read from an article that by the time a baby is three to four months old, it may only take your baby about 5 to 10 minutes to empty the breast and get all the milk he/she needs. 🤷‍♀️

Also, since that appt, I noticed that my LO's nursing habits changed. Instead of drinking long on one boob, he's been drinking around 0-6 minutes from each and has been a bit fussy with nursing (latching and unlatching, refusing nipple/boob, cries after he's done with it). Because of this, I try to give him my slacker boob first which doesn't last long, and then switch to the other one with a faster milk flow. I'm wondering if this change in feeding has anything to do with teething? He's been sucking a lot on his hands, drooling, and sticking his tongue out. Or maybe he's actually still full since I had been increasing the time between feeds (every 1-2 hrs)? Or just overly tired? 🤔 Any thoughts are appreciated!