How to find the costliest layer during Render/RAM preview

Hello Friends,

Situation: I have a 30 layer comp and it does good in RAM previews etc. But suddenly it becomes dead slow for RAM previews or Renders after I added an effect in one of the layers (I forget the layer).

Is there any way we can find out the layer taking the most time other than doing a visibility off for each layer and checking?

In one of my cases I found that a Light layer had Shadows On checked by mistake and was taking lot of time to render. But that took me lot of time to realise, in another case the Shine effect on a 3D stroke was taking lot of time.

Is there a easy way out to find the costliest layer?

Thankx so much.

Tx,
Hafeez