creo3 config.pro option documentation for: PHOTORENDER_PREVIEW_SCALE
photorender_preview_scale
0.5
*
Allows a user-defined size ratio at which Photorealistic Rendering
renders using the Render To
> Full Window (Preview)
setting in the Render Setup
dialog box. Increasing the value creates higher quality rendering with slower performance. Reducing the value produces reverse results. The preview scale ranges from 0.25 to 0.75.
After you set the value, this option takes immediate effect in the current session of Creo Parametric
.