This might depend on the model of DVR (not an NVR?), the type of cameras connected, the settings you have configured on the cameras and DVR, what the storage is, what the firmware is, how you are accessing the DVR etc.
If it's fine over the LAN, and not fine when viewed remotely, yes it could just be overwhelming your upload bandwidth.
What is your broadband upload bandwidth?
If it's fine over the LAN, and not fine when viewed remotely, yes it could just be overwhelming your upload bandwidth.
What is your broadband upload bandwidth?