I am getting problem with rendering including caustic. Basically, when rendering the scene using mental ray without caustic, it merely takes 16 minutes, but I don't know why it takes extraordinarily long with caustic and Global illumination(even the photon emission process already take 40 minutes)

How to render caustic effect faster? I love the caustic effect in the scene. Would you please help me figure out the problem? Thank you

here is the scene that I intend to add caustic. I generate caustic with the table and the window on the wall

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