Thats only enough space for a few hundred chicks. Bobs want about 1/2 sq ft per chick or thereabout. 115 is way too hot. They fall asleep under the light and itll cook them.
How many feeders/waterers are you running?
When someone is seeing large losses of chicks i usually look to enteritis or...
What is covering the floor? Shavings? Dirt?
What is the temperature under the light? What is it in the coolest area of the brooder?
How much space are you keeping them?