f67v2: the lunar - solar tides

[ReneZ]

Three pipes have four faces, one has three. This makes 15. I can't think of anything that's a 15 cycle, unless we're talking of half a lunar month.

Without wishing to argue whether the figure has anything to do with tides or not....

The number 15 is quite relevant for tides.
The main solar tide has a period of 12 hours and the main lunar tide a period of 12.42 hours.
This means that there is a period between two spring tides (i.e. when they add up to each other) of 14.7 days.

This is something that can simply be observed at almost any coastal place, and does not require a physical understanding.