Is there anyone who pays to check the content of text messages from fifteen years ago?

It is basically impossible, unless your phone is still there and the text messages are still on the physical media stored on the phone, then even if the phone is broken and cannot be turned on, there is a way to restore it.

If you want to refer to the information that has been exchanged in the communication operator system, it is impossible. No database is backed up for such a long time. That is to say, you can’t buy back text messages from 15 years ago even if you want to spend money.