Slow SQL transactions over VPN

[xeleron]

Hello dear Softether VPN users, I have a problem with the software. I have a small company to manage of about 7 users. Six of them are local users with one remote. They use an ERP software built on top of MS SQL server express 2012. Everything runs fine and dandy on the lan, but the VPN client is obnoxiously slow. Initially, I thought the problem might be the relatively slow LTE connection of the remote pc (@ 20 mb/s), but I have taken the remote pc to my house where I have a full gigabit contract and connected from there and the slowness still persists. I have conducted speed tests and latency tests through the VPN and the speed and the latency of general use programs is very good (getting @ 180 mb/s ,which is 90% of the main office capacity). Basically everything related to the SQL server itself is very slow, queries are semi decent, but every menu pop-up, or the initial program loading is excruciatingly slow, sometimes waiting for 20+ seconds for the program to load despite being on very potent hardware (nothing is hosted on mechanical hard drives).I checked with the software developer their requirements and they need @256kbps for optimal performance per client. The VPN server runs on W10 machine and so does the client. The server is behind an ISP provided router, with a static address with port forwarding done on 5555. So is the remote client,but the connection is LTE. What am I doing wrong? I noticed the fact that during the program initialisation and running the network traffic is extremely low,somewhere @ 25/30 kbps. Thank you for any feedback.