I bought a 6-month travel eSim. It expires in December, but in September I will likely buy the new iPhone 15. Will my travel eSim transfer to my new iPhone or am I stuck using it on my old iPhone?
No it will not. It depends if the provider you have will let you transfer it. Normally they do not. Just ask them if you could change phone and you would get a new QR Code to add to the new phone when you have your new phone on hand.