F1 orion hybrid 15 week old , when can i harvesting ?

The reason I wrote "past its prime" is due to the fact the plant has basically dropped nearly all of its pistils already, indicating an older plant that is approaching the end of its life.

Without seeing the trichomes under a lense, I can't tell if it fully matured but it's definitely faded out. I'd trim every fan out, cut the base and hang the whole plant at 20deg, 50-55%rh in the dark until the sugar leaves get crispy. Buck the buds into your storage and start burping til ir buds are around 62%rh. Then, id seal the buds up for 3 week monitoring so the rh does not creep up past 64. Then dry them to 58% and enjoy. Past prime? Maybe not. Leaves don't tell me much except it's going to die soon ornin the very least not going to bulk anymore than it has.

Harvest ASAP! This plant is well and truly ready and unfortunately, probably past is peak.