Some people believe this. It’s pretty silly, really, because if you crack your Bible open and spend 5 minutes in it, you’ll see it’s impossible.
The 15th is the first holy day of Unleavened Bread (Leviticus 23:6). It is a feast day, a day in which no work is to be done (verse 7). It was one of seven annual Sabbaths observed in the time of Christ, in addition to the 52 or so weekly Sabbaths.
Mark 15:42 And now when the even was come, because it was the preparation, that is, the day before the sabbath,
Christ was already dead by this point – on the preparation day of the Sabbath. And there is no question that it was the preparation day for the first day of unleavened bread, on the 15th of the month.
John 19:31 The Jews therefore, because it was the preparation, that the bodies should not remain upon the cross on the sabbath day, (for that sabbath day was an high day,) besought Pilate that their legs might be broken, and that they might be taken away.
This wasn’t the preparation for any normal Sabbath day, but a special “High” Sabbath day. A holy day – the first day of unleavened bread. And Jesus was dead and buried before that day arrived. Those who plotted to kill Him made absolutely certain of that!
Mark 14:1-2 After two days was the feast of the passover, and of unleavened bread: and the chief priests and the scribes sought how they might take him by craft, and put him to death. But they said, NOT ON THE FEAST DAY, lest there be an uproar of the people.
If He died on the 15th, He would have died ON the feast day, something the Pharisees took great pains to avoid. There is absolutely no evidence that He died on the 15th, and every evidence that He died shortly after 3pm on the 14th.