Can I turn encryption on/off without causing changes original key

Can I turn encryption on and off without causing changes to my original key? I think the encryption process is causing the slow down when I open my inbox to look at submissions.

Yes, you can retain the same key even if you have your form encryption turned on and off. Just make sure you don't generate a new key so that it doesn't change.

To know more about form encryption, please refer to this guide: Encrypted-Forms-and-How-to-Use-Them