Well first off, if you run an AC you will want to stop running the blowers except for a periodic vent to bring in co2 unless you are using supplemental CO2. You will also probably need a dehumidifier when the lights are off or a controller that will run the blower to remove excess humidity.
Now that we have all that out of the way... on to your question. A 14,000 BTU/hr unit may do the job, not 100% though as I have no experience with the 315w fixtures. I hear they run a lot cooler than HPS. With HPS I would use a 2 ton (24k BTU/hr) for that much wattage. My safe bet is 1.5 tons.
Perhaps someone around here that is running several 315's can tell us how much AC they need to use.