Probably not. Public mobile 3G plans is actually LTE connection capped to 3G speeds. How is your phone set up? Are you manually connected to 3G, LTE or Auto? If you manually connect to 3G network, then you can try to connect to LTE or Auto to see whether it makes a difference (even on 3G plan).
If you have a VoLTE enabled phone, Public mobile has began to switch customers to VoLTE service. This service can be used on the 3G plans also. That may make calling experience better.