Since Android 5.1 is no longer officially supported by Google for security updates, you can improve your app's speed with these steps:
: Customize lock screen visibility to show only the sender, the message, or nothing at all. messenger android 5.1
You must enable "Install from Unknown Sources" in your device's security settings before installing an APK. 2. Use Messenger Lite (Legacy) Since Android 5
The most reliable method for very old devices is using the mobile web version. Navigating to Messenger.com or Facebook.com via a mobile browser like Chrome or Opera avoids app-specific hardware requirements entirely. Troubleshooting Common Issues messenger android 5.1