I worked on delayed notifications. Now, if there is no new notifications when fetching, the delay will increase gradually until reaching every 15 minutes.
As soon as a new notification is received, the app will fetch every 30 seconds and start gradually to increase the delay if there is no new activities.
Also, this delay is reset to 30s as soon as you post for catching quickly interactions.
This is per account, so the app can be active for some accounts and lazy for others.