Royalty 2

15 + 4 = 19

15 - 4 = 11

The Metonic cycle is a period of 19 years (≈ 6,940 days) after which the phases of the Moon recur on the same days of the solar year.

In other words, if there is a full moon on a given date, another full moon will occur on or very close to that same date 19 years later

Exactly 19 years 0 days between Netanyahu winning Israel Election and opening of One World Observatory on Freedom Tower, New York. Of course it was built as a result of 9/11.