Codex Vaticanus and Sinaiticus (late 4th century) disagree with 90% of extant manuscripts. They have faded and have been written over several times over the centuries, making it impossible to know what was originall written on them. Most scholars agree they had at leaast 4 different redactors. They disagree with each over 7000 times! They are loaded with scratchouts, and scratch-outs of the scratchouts. All of this makes it imposible for them to be reliable.
Millions of Christians have good reason to not accept their authiority.
Manuscripts that are far older than Vaticanus and Sinaiticus correcty render the vers as "Lord".
Analysis of Peshitta verse 1Corinthians 15:47
Translations
(Etheridge) The first man who is of the earth is dust, the second man the Lord from heaven.
(Murdock) The first man was of dust from the earth; the second man was the Lord from heaven.
(Lamsa) The first man is of the earth, earthy: the second man is the LORD from heaven.
(KJV) The first man is of the earth, earthy: the second man is the Lord from heaven.