Can a 15 year old have their own Apple ID? Without using family sharing??

Note that the earlier response to your question needs some clarifying.

You do not need to make a separate account when you age out of the "child" category. Just keep on using the one you have.

Depending upon the country you can have your own Apple ID if you are 13 or over. Here is a response by a Community Specialist to a similar question:

"What changes after my child turns 13 if I manage their account ?"

Community Specialist rachaels14 response--> https://discussions.apple.com/thread/254582943

"This will vary depending on your region. However, Create an Apple ID [Create an Apple ID for your child - Apple Support ] for your child provides specific ages depending on country/region you're in when changes would take affect.

"Some Apple ID settings and features work differently for children under 13. For example, a child under 13 can't create an Apple ID without permission and consent from a parent or guardian. The minimum age for account creation may vary across countries and regions as follows: Under 14 in Austria, Bulgaria, China mainland, Cyprus, Israel, Italy, Lithuania, South Korea, and Spain. Under 15 in Czech Republic, France, Greece, Peru, and Slovenia. Under 16 in Brazil, Croatia, Germany, Hungary, Ireland, Kosovo, Liechtenstein, Luxembourg, Malaysia, Netherlands, Philippines, Poland, Romania, Singapore, and Slovakia. Under 13 in all other countries and regions."

After the age listed for your region, your child would have the option to remove themself from your Family Sharing group. Leave Family Sharing covers more about this. Leave Family Sharing - Apple Support

Also, your child would have the option to set up an Apple Music Profile if they're subscribed. See what friends are listening to in Apple Music on your iPhone, iPad, or Android device has more details. See what friends are listening to in Apple Music on your iPhone, iPad, or Android device - Apple Support"

Apart from the above nothing should happen to your phone. However, Apple will require a credit or debit card (usually one of those) be present on your account in order for you to make certain downloads and updates. Unless you live somewhere where you can have one of those at an early age, your parents will have to provide one. They might understandably be leery of giving you unfettered access to their card. In that case you may wish to stay in Family Sharing so they can provide access with the Ask To Buy security for their card.

Yes, you can make another Apple ID on the same device. But you'll have to log out of your current apple ID in settings, then create a new one in iCloud settings.

So yeah, you can just use the same one.