Just found your problem, system was installed by engineers specs!:D
What was the sensible and latent capacities the engineer speced.
How much fresh air is being brought in.
Between the people and hot food, you have around 6.5 tons load.
About another 2 to 3 tons in fresh air.
Then you got lighting load yet. Plus the structures heat gain.
15 tons is cutting it close.
Might be that 15 tons can't handle the peak loads.
Quit screaming and get rid of typing in all caps. It's not only rude it's very hard to read.