I suggest you redo your research into Passover Week. I recently did it and found what I posted. It starts and ends with a high day. Here is what I found.
https://en.m.wikipedia.org/wiki/Passover
Date and duration
See also: Hebrew calendar
The Passover begins on the 15th day of the month of Nisan, which typically falls in March or April of the Gregorian calendar. Passover is a spring festival, so the 15th day of Nisan typically begins on the night of a full moon after the northern vernal equinox.[15] However, due to intercalary months or leap months falling after the vernal equinox, Passover sometimes starts on the second full moon after vernal equinox, as in 2016.
To ensure that Passover did not start before spring, the tradition in ancient Israel held that the first day of Nisan would not start until the barley was ripe, being the test for the onset of spring.[16] If the barley was not ripe, or various other phenomena[17] indicated that spring was not yet imminent, an intercalary month (Adar II) would be added. However, since at least the 4th century, the date has been fixed mathematically.
In Israel, Passover is the seven-day holiday of the Feast of Unleavened Bread, with the first and last days celebrated as legal holidays and as holy days involving holiday meals, special prayer services, and abstention from work; the intervening days are known as Chol HaMoed ("Weekdays [of] the Festival").
https://en.m.wikipedia.org/wiki/Passover
Date and duration
See also: Hebrew calendar
The Passover begins on the 15th day of the month of Nisan, which typically falls in March or April of the Gregorian calendar. Passover is a spring festival, so the 15th day of Nisan typically begins on the night of a full moon after the northern vernal equinox.[15] However, due to intercalary months or leap months falling after the vernal equinox, Passover sometimes starts on the second full moon after vernal equinox, as in 2016.
To ensure that Passover did not start before spring, the tradition in ancient Israel held that the first day of Nisan would not start until the barley was ripe, being the test for the onset of spring.[16] If the barley was not ripe, or various other phenomena[17] indicated that spring was not yet imminent, an intercalary month (Adar II) would be added. However, since at least the 4th century, the date has been fixed mathematically.
In Israel, Passover is the seven-day holiday of the Feast of Unleavened Bread, with the first and last days celebrated as legal holidays and as holy days involving holiday meals, special prayer services, and abstention from work; the intervening days are known as Chol HaMoed ("Weekdays [of] the Festival").
Lev. 23:
5 In the fourteenth day of the first month at even is the LORD'S passover. ( Not the 15 day as your web site states.)
So the medium you posted from doesn't agree with the scriptures here. Passover starts on the 14th day on the month which begins at sundown on the 13th day, and ends at sundown on the 14th day. At sundown, the beginning of the next day, the 15th, begins the High Sabbath, The First day of Unleavened Bread.
6 And on the fifteenth day of the same month is the feast of unleavened bread (Passover is over) unto the LORD: seven days ye must eat unleavened bread.
7 In the first day ye shall have an holy convocation: ye shall do no servile work therein.
8 But ye shall offer an offering made by fire unto the LORD seven days: in the seventh day is an holy convocation: ye shall do no servile work therein.
Remember what Jesus said about the Jewish religious leaders of His Time.
7 Ye hypocrites, well did Esaias prophesy of you, saying,
8 This people draweth nigh unto me with their mouth, and honoureth me with their lips; but their heart is far from me.
9 But in vain they do worship me, teaching for doctrines the commandments of men.
Please let me know if you can see how the website is in error.