Upgrading from iPhone 6s to iPhone 15

I’m about to buy a new phone. Set up looks simple enough till I get to the SIM card. 6s does not support eSIM. 15 won’t take a physical sim. The guidance tells me to convert my existing sim to an eSIM in the old phone before transferring to the new phone -but the technology doesn’t enable this. And I definitely want to keep my existing phone number. Help!