New strain: Can you tell on day 15 of flowering if the strain is a good yielder?

Best thing to do is wait and find out. I once grew a durban poison from Sensi Seeds that left me feeling like a noob. The plant was slow growing, freaking tiny compared to everything else I was growing, and the branches were thin weak linguine noodles. That pathetic looking plant ended up producing beautiful humongous dense colas! Till this day that plant is one of the worst structurally and ironically one of the best yielding.

On a side note, I can always tell when I'm going to harvest ABOUT A POUND...

most seed sellers will tell you what the yeald is you dont have to wait until 15 days of flower....