You might want to play it safe the first time. Nothing worst then finding out that TSA also doesn't think there is a lot of traffic so scales back the lunch time work force.

Unless someone who frequents GSP has direct insight, play it safe, give yourself extra time on this trip and you'll have a better idea for next time.

I haven't flown through GSP for at least 4 years and at the time there were only 6 - 10 people in the security line and I was through in <5 mins but I am sure things have changed since then.