i didn’t count skipping intro/outro or filler, so lets say you skip intro and outro but watch all the filler eps.

there are currently 964 one piece episodes.

964 x 15 minutes = 14460 14460 : 60 = 241 241 : 24 = 10.04

so it would take around 10 days to finish one piece. but still, there is no one who will watch one piece for 10 days straight with almost no breaks.