Doesn't stop drone at Avoid Margin distance

I have configured Proximity sensor for obstacle avoidance function and configured
Avoid enable = 3
Avoid_behave= 1 ( stop)
Avoid_margin = 15 meter( kept high because of flying speed also High)

I was tried to do the Avoid function in loiter Mode at 10m/s speed and drone expected to stop at 15m before the obstacle, but due to high speed the drone could not able to stop at Avoid_ Margin distance and it come very close to the obstacle almost 1meter distance.

If i fly the drone on low speed it can able to stop at desired point some how .

What parameter will make the smoother stop at 15m when flying speed at 10m/s.

How to deaccelarate smoothly?

Change the LOIT_BRK_* parameters

More aggressive stop in loiter mode?

Yeap. And a better PID tuning will also allow you to stop faster.