The read performance from Firestore could be improved by lowering the traffic through the native bridge of RN.
Currently the native code of react-native-firebase is sending documents and changes through the bridge which for large collections causes UI to freeze as it's executed in the UI thread.
This could be improved by keeping documents cache on the JS side and applying only the received changes from the Native Side (Firestore Native Code). This will minimise the traffic through the bridge and will improve the overall read speed.