My iPhone 15 plus is refurbished ?

As a search for that number among known model numbers failed, that must be the serial number. We are not suppoerd to ost serio number here for security reason.

The information stedman1 requests from Settings is this one:

The FIRST character in Model Number shows the phone's provenance:

• M – Brand new device, meaning the device was purchased new
• F – Refurbished device, meaning the device has been refurbished by Apple or a carrier
• N – Replacement device, meaning the originally bought device was replaced by this model likely due to a service request
• P – Personalized device with engraving, meaning the device was customized with an engraving on purchase

If you see the M code on a device sold to you as "refurbished," it was not refurbed by Apple. Not to be trusted.

From where and from whom did you buy it?

It looks like you may have provided a Model Number. If this is correct, the phone is Refurbished

Otherwise, post the Model Number. Settings > General > About > Model Number

That can not be determined by the serial number.

What is the model number at: Settings - General - About - Model = ???