Next time check the detailed headers of the email and you should be able to spot if it's a delay coming out of our servers, or a delay within gmail, or a delay getting from gmail to your phone. The time stamps to troubleshoot this are all in the headers. You might have the "time to sync" set to a long time on the phone, is my first guess. But using Tapatalk on your phone is a far superior option, IMHO, and check it when you can or set up Tapatalk instant notifications.
In general, forum software isn't set up for fast chatting, though.