Can I download the original OX that came with my iPad?

Not that I know of.

Do you have problems with iOS 9.1?

No. you cannot go back to older versions of iOS once you've updated.

For general slowness, try the following steps, and heck between each step:

• A Reset may cure some bugs. Hold down the Home and sleep/power buttons until the apple logo shows up.

  If still not resolved:

• Reset all Settings. Go to Settings->General->Reset->Reset All Settings

  If its still not resolved:

• Restore the device as new.

Use iTunes on your Mac or PC to restore your iPhone, iPad, or iPod to factory settings - Apple Support

This will not install the original iOS, but will restore all settings and refresh the OS in case there was a bug or glitch during update.

"I have 9.2.1" Maybe time to update your profile.

Downgrade to whatever is not supported.

Do you have issues with 9.2.1?