Coverage expired on a new iphone 15

The phone is not "new".

Based on the "5" in the model number, this indicates that the phone was refurbished by a 3rd party company.....not Apple......so it probably does not have any warranty at all.

If the store told you that the phone was new, I would ask for a refund.

Where, exactly, did you buy it?

You didn’t purchase from Apple or an Apple-authorized reseller.

You have no warranty.

Live with it.

What country is that?

It's likely you purchased a gray market phone. Possibly even a stolen device or one that was replaced as defective and not returned to Apple as required.