what is the significane behind the point values in tennis, why 15, 30, 40 as opposed to any other number?

Answer 1

THE SCORES ORIGINATED BY INSPIRING THE CLOCK.

QUARTER--15,
HALF--30,
THREE QUARTERS --45,
AND FULL POINT--(60).

LATER, FOR PRONOUNCING COMFORT, 45 CORRUPTED INTO 40.

Answer 2

The scoring was originally 15 30 45
After 8 sets you would have 360. A full circle

40 was changed later, according to David Feldman, author of the Imponderables series, because 40 was more easily understood over the speaker systems.