What does the number 15 on a geologic map mean?

It depends on the map. There should be a key indicated.

A strike and dip symbol, for instance, is a T-shaped symbol that shows where layers of rock stack up in tilted beds. The number accompanying a strike and dip symbol indicates the angle, or tilt, of the rock bed.

"the socialist system that had been in place had brought economic ruin to the country." i hope this !