iOS 6 FaceTime crashing/freezing with iOS 15 and above

i recently got this ipod touch 4th gen on ios 4.1. i saved the blobs and upgraded to 6.1.6. i was finally able to sign in to facetime after installing a few certificates. however, there is this weird issue when calling devices with ios 15 or above. if you send out a call to them, and they accept, the call will connect. it will freeze after about 5 seconds and the ipod will say "reconnecting". if you receive an incoming call and accept it, it will attempt to connect but it never connects. it will just hang on connecting and just gives up and returns to the facetime app after about 10 seconds. i facetimed my mac running os x sierra and it works normally without any issues. incoming and outgoing calls both work fine. i read somewhere that this is due to the new ios 15 facetime features. is there a way to turn these "features" off or simply connect ios 6 facetime to ios 15 or above?