Background BLE Scan for every 15 min

I have a query regarding Scanning of the BLE devices in an iOS app.

Use case of our app is to share the location of a set of BLE devices assigned to each user continuously to a particular server for every 15 minutes time interval, irrespective of the state of the app (except terminated state may be).

About our BLE device, it transmits the advertisement data once for every 4 second interval.

We tried using the "uses Bluetooth LE accessory" background mode and continuously we were able to scan the BLE devices using the scanForPeripharal method in CBCentralManager with the UUIDs of the BLE devices.

We were able to get the list of scanned devices even in the background.

But when we lock the device and the screen becomes inactive/turned off, we are unable to get the list of scanned devices.

In another solution, we tried using the background fetch but it is very inconsistent(practically it never gets called in the given time interval).

We need a solution using which we should be able to do the following,

For every 15 minutes time interval.
scan the BLE peripherals around our vicinity.

Get the current location of the user.

Share it with a MQTT server.