15 ounces is equal to 443.603 milliliters. To convert ounces to milliliters, you can use the conversion factor of 29.5735296, which is the number of milliliters in one fluid ounce. Therefore, the formula to convert ounces to milliliters is:

milliliters = ounces x 29.5735296

Using this formula, we can calculate that 15 ounces is equal to 443.603 milliliters:

milliliters = 15 x 29.5735296 = 443.603

Therefore, 15 ounces is approximately equal to 443.603 milliliters.