Do I need an ID card to be a temporary worker? (For example, going to RT Mart) If necessary, can I get an ID card at the age of 15?

Of course, if you go to work, you need to show your ID card and register.

15 years old, you can apply for an ID card. You can go to the police station where your hukou is located with your hukou book, and you need to go in person, because you need to take photos on the spot to extract fingerprints.

15 years old, no enterprise is allowed to hire you.