Windell Gann
Tiberius ... Tiberius came to the throne in August AD 14.
The year 15 of Tiberius is thus the year in which Jesus and John alike began their labours.
Since Luke is writing the history of Jesus, and not that of John, this wealth of chronological data must refer primarily to Jesus, and only incidentally to the Baptist. - Caspari, p. 41 [See Caspari p. 42 for greater details of the reign of each of these.]
Luke 3:6
all flesh -- a way of saying Jew and Gentile.
Luke 3:23
Gill suggested the parenthesis should read (as was supposed the son of Joseph) but that Jesus’ first male ancester would be Heli, who was the father of Mary.
Most think that Luke’s genealogy list is via Mary, his real fleshly descent of David, and that Matthew gives his legal genealogy through Joseph back to David.
Luke 3:31
Matthew’s genealogy was through "Solomon"; Luke’s through "Nathan".