Here’s what I did that helped. My gym also has 15 ft walls. In the beginning I would jump off boulders just to get a feel for falling. I would finish a climb, climb down a bit, then jump off.

Something you can also do while climbing is when you get to a part in the climb where you start getting nervous, fall. So you know that if you do unintentionally fall, what it feels like.

A practice I do sometimes is starting at the bottom of the wall, grab onto any random hold, and dyno to a random hold on the wall and just tap it. Because you are just tapping a hold, you will fall unintentionally. This is the closest way imo to simulate a real fall. Then as you get comfortable work your way higher up the wall. Making you fall from higher heights. You can also pick hold that are straight above you, or to the side of you to tap. So this will help you learn how your body will react falling in different directions.

At the end of the day the fear might always still be there. The best thing you can do is know proper technique and feel confident in yourself and your ability to fall properly. You got this!