iPad is very slow charging

Ne aware that most iPad models require a Power Adapter rated to at least 10-12W to reliably charge. 5W Power Adapters will charge an iPad very slowly, if at all. These support pages may help with troubleshooting charging issues:

Charge and monitor the iPad battery - Apple Support

If your iPad won't charge – Apple Support

Troubleshooting generally requires substitution of the Power Adapter and cable for another known-good item.