it always reverts to a 16 digit password which
I'm not absolutely sure, but I believe that, that is just a mask to inhibit guessers.
As far as "slow to receive my mail", I think there could be any number of factors responsible for that (not likely associated with your password).
Speed of computer and how busy it might be, (background tasks)
Speed of internet connection and how busy it might be. (background tasks)
Which mail client are you using?