How to Permanently Delete Text Messages from iPhone 15?

Open the Messages app on your iPhone and navigate to the conversation containing the message(s) you want to delete.

Tap and hold on the text message(s) you want to delete until options appear.

Tap "More" and select the text messages you want to delete by tapping the circle next to them.

Tap the trash can icon to delete the selected messages.

To ensure thetext messages are permanently deleted, connect your iPhone to your computer and open iTunes or Finder (depending on your operating system).

Click on your iPhone and select "Restore Backup."

Choose a backup that was created before the text messages you deleted were sent or received and restore your iPhone from that backup.

It's important to note that restoring from a backup will delete any data, including text messages, that was not included in the backup. Therefore, it's crucial to create a backup before performing this step to ensure you don't lose any important data.

Another way to confirm that the messages are permanently deleted is by using a professional data eraser software.

The tutorial is here:

https://www.safewiper.com/tutorials/delete-imessages-history-on-iphone-ipad.html

Professional software uses advanced algorithms to overwrite the deleted text messages multiple times, ensuring that it is completely and irreversibly erased. This helps to protect your privacy and ensures that the deleted text messages cannot be recovered with data recovery tools. Manually deleting individual messages or performing a factory reset may be time-consuming and may not guarantee complete text messages removal. Using professional software simplifies the process, allowing you to erase a large volume of data swiftly and efficiently.

Permanently remove recently deleted messages and attachments

1. Open the Messages app on your iPhone.
2. In the Messages conversation list, do one of the following: ... 
3. Select the conversations whose messages you want to delete permanently, tap Delete, then follow the onscreen instructions.

Delete messages and attachments on iPhone - Apple Support

Once you delete a text message, it's removed from your visible inbox, but it isn't immediately erased from the device's storage. The space it occupied is marked as available for overwriting. This means that the message may still reside in the phone's memory for a short time until new data overwrites it.

First off, the basic delete is pretty straightforward, right? You just swipe left on the message thread and tap 'Delete'. But that's kinda like tossing papers into a trash can; they're out of sight but not really gone-gone.

To really hammer them into digital oblivion, you'll want to start by deleting the messages or entire conversations just like you normally would. After that, head to your iPhone settings and find the 'Messages' section. Look for the option that says 'Keep Messages' and make sure it's set to '30 Days'. This means that your phone automatically tosses out messages older than a month.