There's a new hidden battery management setting in Android 15 that has been affecting these types of apps, even going so far as to kill them while they are actively playing media.
If you have already taken care of all the typical battery optimization settings, then enable developer mode in settings. I believe you do that by going into settings, then to about phone, then tapping the build number 7 times until you get a pop-up notice that you are now a developer. Then from the main settings screen, go to the System options and you'll find the developer options.
In the developer options, search for one called "Suspend execution for cached apps." It may also be easier to just use the settings search bar because I can search for "suspend" and that pops up as the only result. When you find it, disable it.
This setting is especially important for any streaming app that requires a constant Internet connection. It defaults to on, which will pause active background apps even if they need to remain active (this is different from putting a non-used background app to sleep). I also have to turn this off again after any OS update because the updates will reset it.
It's supposed to help battery life with it on, but I haven't noticed any appreciable reduction of battery life with it disabled.
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