@dtdukes86
I've just discovered the email you sent me a few days ago and sent a reply.
Unfortunately, I'm not sure I can offer much that hasn't already been covered here
In my reply to your email, I asked whether the slow machines are running 32-bit Access and, if so, suggested adding large address awareness.
If that's not relevant, then consider a different file format for the address downloads from Ideal Postcodes e.g. CSV or XML instead of JSON.
However, like the others who have responded, I'm almost certain that the issue lies somewhere on your network
You talked about the speed of large data transfers on your network but the JSON address files involved with this app are tiny Typically 10-20 kB only.
I've attached a zipped JSON address file for a randomly selected postcode as an example
Downloading and processing files such as this really shouldn't cause any issue with modern hardware.