MacBook Neo battery at 100% health after 15 charge cycles

That is normal.

Your battery is fine. Don't waste time worrying about it.

Here is some of Apple's guidance regarding battery performance, health and management:

Batteries - Maximizing Performance - Apple Support

About battery health management in Mac laptops - Apple Support 

In a nutshell, to get the most from your battery:

• Let the OS and charging circuits manage the battery as designed.

• Plug in when using the computer near available power.

• Use on battery when ac is unavailable or when you must be mobile.

• Don’t subject the computer and battery to extreme temperatures.

• Don’t allow the battery to regularly discharge deeply before plugging in. Yes, it may happen from time to time, just don't make it a habit.

• Don’t obsess over battery life and/or health.  

❝Worry is the misuse of imagination.❞ – Zadra

This is totally normal, I also have a Neo and am still at 100% after at least 20 charge cycles.

If you want to increase battery life, some other things you can do are setting a 90 percent charge limit (overridden as needed), using an external power supply when possible, and using low power mode always when on battery.