How to improve image quality

Hi,there
I try to faster faster rendarings with the Cache.


Using this technique, the speed increased dramatically, but the image quality was extremely poor.
Until now, rendering was done in easy setup mode, so I don’t know which parameter to adjust.
Also, I don’t know the appropriate value for resampling filtering radius.
The shadow is not formed.
The object to be rendered is a building.
Thank you for reading.