I checked it. - I could be wrong but...
24' (pool Diameter in ft) / 2 = 12' (Pool Radius in ft)
PI * 12' (Pool Radius in ft) ^ 2 = 452.39 (Pool surfdace area in sq ft)
4' (Pool Depth in ft) * 452.39 (Pool surfdace area in sq ft) = 1809.5 (Pool Vulume in cu ft)
809.5 (Pool Vulume in cu ft) * 7.48 (Gallons in a cu ft) = 13,536 (Gallons in Pool)
15 (Gallons of LC) * 12.5% (Concentration of LC) = 1.875 (Gallons of pure LC)
1.875 (Gallons of pure LC) / 13,536 (Gallons in Pool) = 0.0001385 (fraction of LC in pool)
0.0001385 (fraction of LC in pool) * 1,000,000 = 138.5 (parts per million LC in pool)
I know it's supposed to be done by weight but ... DANG that's alot of bleach!

Please check it. Look around this forum for help on reading high cl levels.

If stuff in your pool really consumed that much chlorine and your level really is 1.0, you'll need to bring that up but you really need the advice of somebody here with real experience to help you figure out where you are.

You need to figure out where your FC and CC really are.