How does the layer style change the speed of Photoshop?

I assumed the pattern size, the number of layers, and the image size will slow down the software. However, I found the order become confused, as I do more and more work.

The same pattern, be used in different renders, one of them, which has 14 pattern layers, 3500x4000 pixels, takes 17 seconds to change the pattern data, the other render, which has 17 pattern layers, 6000x5000 pixels, takes 6 seconds to change the data. Why is that?

HELP! PLESASE!