Check the code snippet and API documentation carefully. There is a property inside of configure called minimumFetchInterval. You can adjust the value and check if it works, should work.
api-doc Following code snippet is placed under Android part in api doc.
BackgroundFetch.configure(BackgroundFetchConfig(
minimumFetchInterval: 15, // <-- minutes
stopOnTerminate: false,
startOnBoot: true
), (String taskId) async { // <-- Event callback
// This callback is typically fired every 15 minutes while in the background.
print('[BackgroundFetch] Event received.');
// IMPORTANT: You must signal completion of your fetch task or the OS could
// punish your app for spending much time in the background.
BackgroundFetch.finish(taskId);
}, (String taskId) async { // <-- Task timeout callback
// This task has exceeded its allowed running-time. You must stop what you're doing and immediately .finish(taskId)
BackgroundFetch.finish(taskId);
})