PhoneRTC iOS demo too much video latency

I download demo of PhoneRTC in https://github.com/alongubkin/phonertc/tree/master/demo

But unfortunately, PhoneRTC video latency is too long, also video picture is broke.

App is run on iPhone 6.

I run Turn server on AWS EC2 and Signaling Server on local.

And I proceed 2 test with 2 phone is in same network and other network. But All are same

In android, It works well. but not in iOS

Is this phenomenon normal? or Do I do something wrong?