@Ratna8 I also had my text notifications stop a couple years ago. It took them about a month to get them up and running again. Now I mostly get them, but they are sometimes erratic- the latest booking request I got I never received a notification of, but I got notifications of the 2 message responses I got from the guest after accepting her booking, just a short while later.
I'm not sure why hosts think they have to check every 15 minutes, though. I never answer my phone at night after I've gone to bed- I turn my ringer off. And I have another job, so I've often not responded to a request for several hours after it came in and I've never lost a booking because of it. If it's a matter of guests who are already staying needing your asistance, I'd just explain to them that your notifications aren't working, and if it's an emergency, to please contact you via text message or phone call. Also, set your email so you get notifications on it, and if you get a message, you will see the notification on your email.
The idea that hosts have to check their messages every 15 minutes is absurd to me- I do this as a pleasurable experience, not to be a slave to it. Checking twice a day, in case notifications aren't working, seems quite sufficient to me.