Usually the hops are added in the kettle. It can also use hop back to add hops after whirlpooling to add flavors.
But if I want to steep the hops for 15 minutes? And also want to add the flavors of the hops. I will need to cool the wort first?

Answer: if you want to steep the hops for 15 minutes, we have talked and we can add the cooling jacket on the whirlpool tun and cool the wort first. Then add hops in the whirlpool tun. Customers usually add hop pellet in whirlpool tun.

The hop back is usually used for fresh hops.
If you do not use the hop back but add pellet in the whirlpool tun, then we can add a Y type filter to avoid some impurities going into the heat exchanger. Please check the attached picture.

We have another customer who just confirmed the order are using the similar ways to add hops. At last he chooses to cool the whirlpool tun.

Hope this helps you!
Thanks for your reading.
Thanks for reading.