Hi TC,
There's some funny theories out there about this. One is that Jesus was observing the passover when the Essene/Qumran sect normally would, which would have observed Passover one day earlier than the Jews would have in this case. I don't think there's much merit to that one though. Even though I think Jesus ate his Passover earlier than the Jews in this case, I don't think it was because the Essenes did so.
I think that Jesus probably observed the passover on the same day that the Jews may have in one sense though, well.. kind of. Jesus and his disciples ate the Passover on the 14th of Nisan. Once the sun had gone done, technically the next day had begun on the Jewish calendar, and it was the day of preparation for the The Feast of Unleavened Bread, which is the 14th, when Jesus and his disciples were eating. The Jews then most likely killed the sacrificial lambs the afternoon of that same day, and then sat down and ate the Pesach (Passover) meal right as the sun was going down. So they ate the Passover on the 14th/15th depending on how you look at I guess. Jesus and his disciples ate the Passover a little less than 24 hours before the Jews did though, at least I'm pretty sure of that. I don't think any other Jews ate their Passover meal at the same time Jesus did, but instead not till later that same day, right before the sundown which went into the 15th of Nisan.
When the lambs were being sacrificed for the Passover, the Lamb of God was being sacrificed as well, for our sin. The blood of bulls and goats cannot atone for any sin, neither can mere earthly sheep. But the body of our Lord was prepared for him, and he came to earth to die on a cross to atone for our sin. We needed a sinless and perfect Lamb to do the job, and there is only one of them around.
So, Jesus's disciples observed two Passovers that day. The first they observed in the natural, the second was spiritual. Jesus was their Passover lamb and they ate his flesh and drank his blood, spiritually speaking. When the Jews were eating their Passover meal in the natural, Jesus's disciples were eating their passover meal in the Spirit. They just didn't know it at the time. All who believe on the Lord Jesus Christ take part in his death, and will take part in his resurrection as well when he returns a second time. Part of taking part in his death is to feast on his flesh and his blood. The Jews who didn't believe only had physical flesh to feast on, but the disciples who believed had spiritual flesh and blood to feast on, as all of Jesus disciples still have to this day. Jesus physically died and shed his blood on that cross that day, but we do not eat his literal physical flesh and his literal physical blood, unless one is Catholic I guess...
John 6 KJV
53 Then Jesus said unto them, Verily, verily, I say unto you, Except ye eat the flesh of the Son of man, and drink his blood, ye have no life in you. 54 Whoso eateth my flesh, and drinketh my blood, hath eternal life; and I will raise him up at the last day. 55 For my flesh is meat indeed, and my blood is drink indeed. 56 He that eateth my flesh, and drinketh my blood, dwelleth in me, and I in him. 57 As the living Father hath sent me, and I live by the Father: so he that eateth me, even he shall live by me. 58 This is that bread which came down from heaven: not as your fathers did eat manna, and are dead: he that eateth of this bread shall live for ever.
Grace to you,
Travis