第一个ajax调用速度非常慢，后续调用运行速度很快——为什么?

I'm using a simple jQuery AJAX function that runs extremely slow (10-15 seconds) the first time it's called, and then runs normally at <1 - 2 seconds each time it's called after that first time. I cannot figure out why this is happening but need to speed it up as much as possible. Here is the function:I'm using a simple jQuery AJAX function that ru