Tax and NICs on additional earnings

I have a full-time job but plan to start a tutoring service in the evenings and at weekends. It is likely to generate about £15000 per year. Will it be better simply to declare these extra earnings to HMRC using an appropriate form or set up as a sole trader and pay that way? Does one method have advantages over the other? Thank you for any advice you can give.

Hi,
As this would be seen as self employment, you will need to register for self assesssment and declare the income in a tax return.
Thank you