The context of Deuteronomy 16:1-3 indicates the focus of these verses is on the Night to be Observed and the Days of Unleavened Bread rather than the Passover.
The proponents of a 15th Passover discount clear scriptural details and instead speculate. One cannot build doctrines on implication, distortion, and traditions.
Nine steps had to be included with the Passover observance, all within the house until morning. It takes place between sun's setting and complete darkness.
God never says the Christian life would be easy or that life would always be fair. Difficulties and tests are given to test our hearts and promote humility.
Like the Old Testament examples, the Corinthians had a careless presumption, allowing themselves to lust, fornicate, tempt God, and murmur.
If we, like Israel of old, choose to sin, we will receive the same consequence. Two thirds of the book of Numbers emphasizes that if we sin, we die.
The trials we go through are part of His providence, putting us into humility and determining what really motivates us.