WhatsApp for Samsung Galaxy J2 (2017)

The J2 (2017) shipped with only 1.5GB of RAM, so WhatsApp plus a couple of background apps will choke it. Clear room by going to Settings > Apps > WhatsApp > Storage and tapping Clear cache, then disable bloatware you don't use (Settings > Apps > select the app > Disable). You can also speed up the UI by unlocking Developer options (Settings > About phone > Software information > tap Build number seven times), then going to Settings > Developer options and setting Window animation scale, Transition animation scale and Animator duration scale to .5x. Turning off WhatsApp's media auto-download (WhatsApp > Settings > Storage and data) also helps. See how others solved this on Reddit

The 16GB of internal storage fills fast, and WhatsApp media is usually the culprit. Insert a microSD card and move photos/videos there via Settings > Device maintenance > Storage, and in WhatsApp go to Settings > Storage and data > Manage storage to bulk-delete large forwarded videos and files. Also clear the Play Store cache (Settings > Apps > Google Play Store > Storage > Clear cache) so updates can install on the limited free space. See how others solved this on Reddit

The J2 (2017) runs Android 7 (Nougat) and never got major OS upgrades, so newer WhatsApp builds increasingly drop support for old Android versions. Install any remaining system updates under Settings > Software update > Download and install, but on the OS side there's no real fix. Back up your chats to Google Drive before support ends and plan to move to a newer phone; once WhatsApp drops your version you'll eventually be unable to send or receive messages. See how others solved this on Reddit

Back up first by opening WhatsApp > Settings > Chats > Chat backup and tapping Back up to Google Drive (make sure the J2 is signed into your Google account under Settings > Accounts and backup). On the new Android phone, sign in with the same Google account and phone number, and WhatsApp will offer to restore that Google Drive backup during setup. If you're switching brands, you can also use that maker's transfer app, but for WhatsApp specifically the Google Drive method is the most reliable. See how others solved this on Reddit

Samsung's aggressive battery management can kill WhatsApp in the background on these J-series phones. Go to Settings > Device maintenance > Battery and make sure WhatsApp isn't on the sleeping/unmonitored apps list, then go to Settings > Apps > WhatsApp > Battery and set it to not be optimised. Also confirm notifications are allowed under Settings > Apps > WhatsApp > Notifications so calls and messages still come through with the screen off. See how others solved this on Reddit

Custom ROM support for budget J2 (2017) variants is very limited and mostly unofficial, so there's rarely a stable LineageOS build, and flashing trips Samsung's KNOX permanently and voids the warranty. Before trying anything, fully back up WhatsApp to Google Drive (WhatsApp > Settings > Chats > Chat backup) because flashing wipes the device. For most owners the safer path is a clean factory reset (Settings > General management > Reset > Factory data reset) plus a microSD card rather than risking a ROM on such old hardware. See how others solved this on Reddit