Problems while transferring data to new phone

I just got my 256 GB iPhone 12 and am transferring data from my 256GB iPhone 10. My iPhone 10 is nearly full because I have lots of media. The transfer has been going on for 9+ hours and the bar on the screen shows no progress, but when I tell it to Cancel, it asks me if I want to cancel the transfer--so the phones are not locked up. Is it possible that a phone that is nearly full of data would take this long to transfer? I think something is wrong because the progress bar shows no progress. Should I start over?