My iPad continues to give me error TS4515. , load iPad to my grandson , for games

The only reference I could find with that error code is this article

Turn off Find My iPhone Activation Lock - Apple Support

You will need to contact your grandson and have him get rid of the activation lock.

FWIW, I would not loan any of my Apple devices to anyone.

Where exactly are you seeing this error, and what are you trying to do when you see it? What are you referring to when you say that "grandson got it back"? Did you have this device serviced somewhere, and if so, by whom?