How to optimize Firestore read/write operation - firebase

Question

I try to make Stock monitoring app where users can make Alert when price change.
I have Stock document where I fetch from 3rd party API periodically.
Upon Stock update I fetch all Alert which meet condition and notify users with Firebase messaging.
Here is my models.
/stocks/{stockId}
id: String
price: Number
/alerts/{alertId}
stockId: String
price: Number
condition: [moreThan, lessThan]
uid: String // User who create alert
/users/{userId}
id: String
fcmToken: String
Every 5 minutes I fetch latest stock price and update stock document = number of stock write query.
function updateStockPrice(): Promise<FirebaseFirestore.WriteResult[]> {
const db = admin.firestore();
const options = {
// Options for stock api
};
return client(options)
.then(function(body) {
let batch = db.batch()
for(var stock in body){
let data = // create data from json response
let docRef = db.collection("stocks").doc(//id from 3rd party api)
batch.set(docRef, data)
}
return batch.commit()
});
}
On stock write update, loop through alerts and fetch fcm token from related user to send out push notifications = (alert query + number of alerts matched condition for user query) x number of stock update
export const onStocksUpdate = functions.firestore.document('stocks/{stockId}').onWrite(function(change, context) {
const db = admin.firestore()
const newValue = change.after.data();
const previousValue = change.before.data();
const stockId = Number(context.params.stockId)
let p1 = db.collection("alerts")
.where("stockId", "==", stockId)
.where("condition", "==", "moreThan")
.where("price", "<=", newValue.lastPrice)
.get()
.then(function(querySnapshot) {
const promises = []
querySnapshot.forEach(function(doc) {
let data = doc.data()
let user = db.collection("users").doc(data.uid).get()
user.then(function(snapshot) {
let userData = snapshot.data()
return userData.fcmToken
}).then(function(fcmToken) {
const payload = {
notification: {
title: // title,
body: // body
},
token: fcmToken
}
return admin.messaging().send(payload)
}).catch(function(error) {
console.log(error)
})
promises.push(user)
})
return Promise.all(promises)
}).then((response) => {
// Response is a message ID string.
console.log('Successfully sent message:', response);
})
.catch((error) => {
console.log('Error sending message:', error);
});
return p1
})
Total write = number of stock
Total read = (alert query + number of alerts matched condition for user query) x number of stock update
Say I have 20 stocks, 1 user with 3 alerts.
Each 5 minutes I will use 20 write query and (1 + 3) x 20 = 80 read
In 1 day = 5760 write and 23,040 read
This seem too much operations for such a small examples. Is this the right way I should lay out data structure? Or is there a better way to do this?