Slow conversion

When I select a new style it takes several minutes to see the results…? Is this normal.
My PC is win10, 64, Intel i7, 16mb RAM and Nvidia 1080 graphics

Presets using AmbientOcclusion (most of them have a “AO” in their name) can take long time to render. You can try lowering the resolution: just clich on the resolution tool and set max viewport resolution to 1MP.