the IPadOS 14.3 won't update on my ipad. seems to be very slow. Any suggestions?

The update, already downloaded, cannot install. This update file may be damaged/corrupted. You need to delete the update package - and then download a fresh copy of the update.

To delete the failed update from your iPad:

Settings > General > iPad Storage

Scroll down the list of Apps until you find the Apple Update, tap, then select Delete Update.

After deleting the update, a forced-restart of the iPad is recommended:

• On an iPad with a Home button: Press and hold the top button and the Home button at the same time. When the Apple logo appears, release both buttons.
• On an iPad with Face ID: Press and quickly release the volume up button, press and quickly release the volume down button, then press and hold the top button. When the Apple logo appears, release the button.

After restarting, you can reattempt the update:

Settings > General > Software Update

I hope this proves to be helpful in resolving the problem.