I will say much much better and Paul I guess will say much much worse
We had real issues with imap, EAS, folder management and other items on V15 for us it was awful
Since moving to 16 we have had no real issues
We have a mixture of customers and domains who use imap, Outlook and the web interface both on the desktop and mobile
The web interface seems popular with customers on their tablets for Mail Calendars etc and have a few 100 who log into that constantly