Everything seems to indicate that iOS 15 has more problems than we would like and one of those big problems is that Notification sounds are not heard How can we solve it? Do not worry, a little further down we are going to investigate several possible solutions to this problem.
Notification sounds are not heard in iOS 15
Adjust notification settings
We go to “Settings” on our device and look for the “Notifications” section. After this we will have to choose the application to which we want to customize its notifications. We will be able to enable or disable sounds, hide previews on the lock screen or adjust the grouping of notifications.
Turn off focus mode or do not disturb
It is essential that we check that the focus or do not disturb mode is deactivated if we want to receive notifications. This mode serves precisely to prevent notifications from bothering us.

For this we will have to go to Settings> Focus. Once we are in this section, we are going to turn off the focus mode switch.
Update apps

If we have not updated the application where the notifications fail it may be because it is with an outdated version. Updating the app can be the solution to these problems.
To do this we go to the App Store and we will have to click on the profile icon that is in the upper right corner of the screen. Then we scroll down and can update one app at a time or update all of them at the same time.
Disable summary of notifications
Another reason why we can’t hear notifications could be because of the Notification Summary option. If it is enabled, then it will end up showing all notifications at a specific time, so we must be sure that it is disabled.

For this we are going to go to Settings and choose Notifications. Next, we select the option “Scheduled summary” and deactivate it.
Reset all settings
We can’t deny it, factory reset is the universal solver to the vast majority of software-related problems.

We are simply going to go to Settings> General. Then we choose Transfer or reset iPhone and then Reset all settings. It will ask us to enter the device password. A window appears at the bottom with several options, we are going to choose “Reset all iPhone settings” and wait for the device to restart.