ok, those are 5MP cameras on an NVR that supports up to 8MP so it is unlikely to be a bandwidth issue with the NVR, although saying that the limited specs I found online do not tell me what the incoming/outgoing bandwidth capacity is and I wouldn't be surprised if it is very low for this consumer range product. Potentially you could try lowering the resolution, reducing the fps, and the video quality to limit the outgoing bandwidth and see if that improves the remote connection.
Other than that my only other recommendation would be to check for latest firmware or poor/slow internet at the remote location where you try to access the NVR.
As I have already said we don't work with Pyronix equipment so you will have to contact them directly for the latest NVR and camera firmware.