bad audio messenger facebook iphone 6s

when im in a video call the audio is terrible but if i change for my mom iPhone 5s which is running the same iOS there is not bad audio or if i call through Facetime from my iphone 6s th same thing only with my iphone 6s and facebook messenger video call

is somebody else with the same problem

I Think that is a facebook problem specifi for iphone 6s because is only with the messenger