Since it works fine on your LAN there must be something about how the data passed through the cell network. JRemote doesn't do anything different based on whether the connection is a LAN connection or WAN connection.
Download tests over the cell net aren't very useful in this case, there are plenty of operators that take that info into account and provide short bursts of high speed to make a connection look good. There are also lots of QOS operations going on for various services.
It's possible that the connection on port 52199 simply isn't allowed full bandwidth.
If you aren't running a webserver on your home connection you might try changing the forward on your router to go from port 80 to port 52199 on your MC PC and add a server via IP address and port in JRemote to see if that makes any difference.
Of course make sure you have a strong login/password for any remote access.
I've done several hours of experimenting, and I am more confused than when I started.
Briefly, it is not MC doing this, the same is happening to my PLEX. My server computer is the only one having this issue, if I stream media files from any of my other machines it being windows or mac I get above half of my theoretical upload speed of my home connection even over LTE to my phone, but that specific server MC is running on seems to cap the speed specifically at 2.0Mb/s, but I noticed I managed to barely realtime stream 96/24 when connected to a wifi at a hospital today so something is for sure the issue with my ISP in addition.
But here's one of the many things that are weird: Upload from MC to LTE seems to cap at 2.0Mb/s, to a home connection 3 - 4 Mb/s ish, and when downloading using filezilla all my tasks caps at 1.3MiB/s, and tried to upload a file to a friend's FTP server from my own server and it also capped at 1.3MiB/s, and downloading from a test FTP on chrome seems to cap at 2.0MB/s, but I get 30+ on my other machines on the exact same file. I've changed all kinds of settings on the network adapter, jumbo frames, power saving features, I've tested every single one one by one following guides, including trying another network card entirely. I've turned on and off firewall as well. I got hold of the latest intel drivers for the card too, no change. I've experimented with QoS settings on my router, all machines are running @ 1GbE between eachother. Just to add, I'm not disk read/write limited either.
Yet to test: USB tethering the server and see if i can rule out my router somehow discriminating that machine in particular, boot linux from a pen without installing and rule out my windows 7 install having an issue, being misconfigured a spot I have overlooked or if I am CPU/hardware limited in any way. (i-7 4790k, ddr3 2133mhz) I have the exact same network adapter on my gaming windows machine and that computer has no issues with FTP or MC speeds.
