I also believe it was the preperation day (14th) followed by the 15th, and the 15th was a Sabbath (7 th day of the week) which was also a "high day" and the "Passover".
Scripture is fairly clear that the crucifixion was on a Friday. Before Friday would have Jesus rising on a day other than the 3rd day. And we know He rose on the 1st day of the week.
The question becomes whether we believe that the Gospels record 1st century historical events or were referencing the OT to provide a timeline.
My opinion is that the Gospels recorded what occurred (what they observed) in the 1st century AD and that the crucifixion occurred at a moment in history (a real historical event).
The opposing view is that the Gospel accounts ignored 1st century historical events, what was actually occurring in and around Jerusalem, and instead used the OT as a type of code to date the events surrounding the crucifixion.
Where does the word of God say he, "rose ie was made alive out of the dead ones," the first day of the week? I believe that was, the state of Jesus, early morning while yet dark on the first day of the week but not necessarily when he was made alive out of the dead ones.
And the sabbath having past, Mary the Magdalene, and Mary of James, and Salome, bought spices, that having come, they may anoint him, Mark 16:1
With a doubt after the women saw where they laid Jesus just before the beginning of a sabbath and
after that sabbath was past the women bought spices and prepared them.
We are also told that, the women rested the sabbath, per the command, after preparing spices.
That can only happen if there is a day of rest, no work, followed by a work day, followed by another day of work, no work.
He was gone from the tomb when they got there because he had been raised, the third day.
The third of a day like spoken of here.
Jesus answered, 'Are there not twelve hours in the day? if any one may walk in the day, he doth not stumble, because the light of this world he doth see;
Friday to while still dark on Sunday ain't going to get it.