Prepass problem

[pabloreyes]

Question and problem, when i use a first render prepass (1-2) This does not delay anything when I open program and rendering, but when I render animation frame 0-50 or any, this prepass begins to increase and take more and more, the render always 15-20 seconds(last pass), but the prepass(1-2) increases each time more, say when it comes to frame 85 - render delay 1-1.20 min, then closed program and i open, render in frame 85 to test and prepass does not delay nothing total render with prepass 18 seconds, what happens?? Is my computer? Is the vray without original license or what?

 

need help really.