Google Calendar Refresh time

I use Google accounts for my daily schedules and I also use the  Calendar on my iPhone. But I notice it takes a long time to sync events I create or delete (or won't sync at all) on my iPhone's  Calendar. It's set to fetch every 15 minutes in settings. Should I leave it on Automatic? It says that for it to push automatically, the iPhone needs to be on power and on WiFi, which is not the case - my iPhone is on battery.

Does anyone know what could solve this issue?