Rendering an image slow at beginning I have a problem with rendering a certain scene in the cycles engine. When I press the render button, it seems like before any tiles are rendered, Blender stays stuck at the grey screen for quite a long time before starting to render any tiles, where it proceeds to render at a reasonable speed. Even when I change from solid view to rendered view, Blender stops for a little while before beginning to render. Is there a certain cause for this? My scene has about 150,000 verts in total. 

Any help would be greatly appreciated. Thanks!
Cycles needs to cache the scene into memory, this takes time, see: https://blender.stackexchange.com/a/31976/21508

That answer also correlates with your question.