15. A bouncy ball falls from point $A$ to the ground, bounces up to point $B$, then falls to a platform $20 \mathrm{~cm}$ high, bounces up to point $C$, and finally falls to the ground. Each time it bounces, the height it reaches is $80 \%$ of the height from which it fell. It is known that point $A$ is $68 \mathrm{~cm}$ higher above the ground than point $C$. Find the height of point $C$ above the ground.
Three, 15. Let the height of point $C$ above the ground be $x \mathrm{~cm}$, then $\frac{\frac{x-20}{80 \%}+20}{80 \%}-68=x$. Solving this, we get $x=132$. Answer:略.

Note: The word "略" at the end is not translated as it seems to be a placeholder or abbreviation in the original text, possibly indicating that the detailed steps or further explanation are omitted. If you need a specific translation for "略", please provide more context.