Error 15 on the Segway KickScooter P65 means “Brake Hall sensor abnormality.” Most likely cause: a brake lever that doesn't return fully, or a faulty brake sensor. Try this first: check the brake levers spring back.
Brake levers have sensors that tell the motor to stop when you brake. This code means the signal looks wrong. Check your brakes work properly before riding.
Step-by-step checklist
Work from the top. Steps go from free and easy to shop jobs. Switch the scooter off before touching any connector. Tick each step as you go. Your progress is saved on this device.
When it's time for a shop: if you've worked through every step and the problem is still there, contact the brand's support or an authorized service center. Bring your notes on when it happens, plus the code.