How to secure my iPhone 15 Plus from Virus?

Those are scam messages. A non-jailbroken phone cannot be hacked, get a virus, or malware. Ignore them.

Scam.

If the messages tell you to call a number, do not call the number. Anyone can include their own phone number in a bogus "security" message, and this is how criminals get you to deliver yourself into their "tender", "loving" hands.

If the messages tell you to install a "security" app, do not install that app.

Blocking spam/scam e-mails and text messages is a bit like a game of Whack-a-Mole, but for whatever it's worth:

Block, filter, and report messages on iPhone - Apple Support

There are no viruses capable of affecting your phone.

Where are you seeing the bogus messages?

While surfing?

While using an App/Game?

shelina69 wrote:

Always in my messages!!

If they are appearing as text messages, it would seem the only course of action is to block and report as junk. Do not interact with the sender, as that would signify to the scammers that you have an active number.