I understand we are getting personal about our phones and have our - sometimes - unique expectations.
There is a dedicated thread on memory management issues linked to Android 15 - that is why I asked - with the company representatives confirming looking into it.
https://forum.fairphone.com/t/fp5-android-15-killing-background-apps-more-aggressively
But some users - included myself - are not experiencing that. My apps (apart from Spotify) do not usually close and I am able to complete most of my actions (payments, authentification, shopping). Hard to say how I would feel otherwise, perhaps would struggle like you or look for some radical solutions (a factory reset might be one).