Most infusion nurses are paid hourly. Discover Nursing reports that the average salary of an IV therapy nurse between $44,000 and $57,000 a year for 2013.
There are 10ml in a dessert spoon. (And 5ml in a tea spoon.) There are 10ml in a dessert spoon.
So you have 15 milligrams in a spoonful of 5 milliliters. That is a concentration of 5 milligrams per milliliter which we can write as 5 mg/ml. A fluid ounce has 29.57 ml so 4 oz = 118.28 ml and that would have 591.4 mg of ingredient. Go to http://wolframalpha.com/ for conversions and to check arithmetic.