Slow delivery of Firebase Push Notifications

I use Firebase Cloud Functions which listen for Firestore changes and send push notifications accordingly. However these notifications are very slow. They arrive to end user with almost a minute delay. For chat application which I'm creating is not so good and should be instantly.

This is the code from Cloud function which does listening and sending the notification:

              admin.firestore()
              .collection('users')
              .where('id', '==', idFrom)
              .get()
              .then(querySnapshot2 => {
                querySnapshot2.forEach(userFrom => {
                  console.log(`Found user from: ${userFrom.data().nickname}`)
                  const payload = {
                    notification: {
                      title: `You have a message from "${userFrom.data().nickname}"`,
                      body: contentMessage,
                      priority: 'high',
                      badge: '1',
                      sound: 'mytone'
                    }
                  }
                  // push to the target device
                  admin
                    .messaging()
                    .sendToDevice(userTo.data().pushToken, payload)
                    .then(response => {
                      console.log('Successfully sent message:', response)
                    })
                    .catch(error => {
                      console.log('Error sending message:', error)
                    })
                })
              })

Is there a way to improve this?