Tribulus dose?

I posted this in supplements forum, but then noticed the whole thing is full of spam. That subforum used to be legit, wtf happened?

anyways:

I been taking this stuff, 1,500 mg/day

https://www.amazon.com/Tribulus-Terr.../dp/B01M26LT35

I'm looking to buy more, and I see this, 15,000 mg/day:

https://www.amazon.com/Tribulus-Terr.../dp/B0845W3R7N

a lot of brands are selling 1,500 mg but a couple are selling like 9,000 or 15,000.

What is an appropriate dose, and why is there such a variation in dosage?