Nanchang No.15 Middle School is better than Zhixing School. Nanchang No.15 Middle School is a public school, and Nanchang Zhixing School is a private school. Nanchang No.15 Middle School has the following advantages over Zhixing School:

1. School type: Nanchang No.15 Middle School is a public school, and Nanchang Zhixing School is a private school.

2. Faculty: The faculty of Nanchang Zhixing School is relatively small, but teachers generally have high academic qualifications and rich educational experience. Nanchang No.15 Middle School, as a public school, has a strong faculty and rich qualifications and experience.

3. School facilities: As Nanchang Zhixing School is a private school, its facilities and resources may be relatively limited. As a public school, Nanchang No.15 Middle School usually pays more attention to investment and construction, and has relatively perfect teaching facilities and resources. To sum up, Nanchang No.15 Middle School is better than Zhixing School.