I hope the wording isn't too crass, but I've found asking for general advice gets me little attention.  So I'm trying to entertain and enthrall.
I have a PDM Standard implementation with three users and a server.  The server is a Windows 10 Pro station with the DB, Archive and license server installed. The server is on a router connected to the internet through a cable modem with a dynamically assigned IP address.  Clients connect to the server over VPN.
The server runs SoftEther VPN-which is an open source VPN software and dynamic DNS provider.  The VPN server software takes care of all of the routing through the firewall.

The client machines are all Windows 10 Pro, running Softether VPN client programs.

This freeware, consumer-level VPN topology works.  It's just not that great.
I mean, compared to Dropbox, this thing is a dog.  If the client computers are are the same subnet as the server, performance is fine-not as fast as moving files through windows, but definitely quicker than internet downloads. But as soon as the client machine is on VPN, it's hit or miss if I'm going to be able to download the latest version of an assembly tree in a reasonable amount of time.  A 45Mb assembly can take an hour to refresh-or it might take 10 minutes.  In the mean time, Dropbox refreshes in a couple of minutes.

I can't manage projects on Dropbox.  So my goal is to improve my VPN configuration so that PDM Standard works better.
I'm just not sure where to begin.

Most of the time, when I look for articles and advice on configuring VPN connections online, the answers are geared towards achieving connection anonymity or streaming Netflix.  So I don't know if I should find a better DDNS service or use my ISP's VPN hosting service.
I'm requesting that anyone who's set up and run a VPN environment for multiple PDM users tell me what's wrong with my hardware, network or thinking.

Thanks

John