If you are saying that the pond at full capacity is 15 feet deep, then you're not at risk of going totally dry. Ponds at 12 feet are normally safe, so you're in the clear.

Of course, that all depends on the soil and watershed. Assuming that these two variables are satisfactory, then you'll have a wet pond for a long long time.

0.6 acre pond / 13' max depth / Bonham, TX