my old iPhone 8 won't allow me to erase my phone and it has a 15 minute wait

I understand that you are referring to the passcode that is used to get to the Home Screen of your iPhone. You will have to reset the passcode to your iPhone by following the instructions in this guide published by Apple 👉 Reset the Passcode of your iPhone (Without a Computer).  Note: All the data on your iPhone will be erased.

Axel F.

Mrenteria01 Said:

"my old iPhone 8 won't allow me to erase my phone and it has a 15 minute wait: how to erase iPhone while on a 15 minute wait?"

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Set this Up Anew:

Set this up anew, as if you were to sell it. Perform as instead here, including the iCloud logout:  What to do Before you Sell, Give Away, or Trade in your iPhone, iPad, or iPod touch - Apple Support. Backup what need be, prior to performing this. All would go to default, and the prompt would be expected to go away.