Samba Slow on OpenVPN

In order to access my home network when travelling, I use OpenVPN, which I host on the same Raspberry Pi that I host OpenMediaVault on. This is very conveinent because it allows me to access my Samba shares while on the road, and while it works, I've noticed a problem with slow transfer speedsr reaching 6Mbps tops when I know that both my home network as well as the network from which I am accessing is capable of speeds much greater than that.

Unfortunately, although using FTP would be the advisable thing to do here, I have limitations that prevent me from doing so. Is there something I could do to fix the problem?

The Raspberry Pi in question is a Raspberry Pi 3 Model B. Do you think overclocking the Pi could help? If yes, how much should I do it? I don't want to do more than is necessary.

Update: I have tried overclocking, but the issue is not resolved. I read online that packet fragmentation could be the issue, but I have no idea what that is or what I can do to fix the problem. I question whether the Pi is the problem or not simply because speed tests work just fine.

Very well. Instead of doing that, I am going to instead set up a VPN on another machine and tunnel my way to the Pi through that. If what you say is true, that should solve the problem.

Unfortunately, setting up a VPN on another machine on the network did not solve the problem. The transfer is still slow.

The server's connection averages 50Mbps for both upload and download. The client connection averages 15Mbps download and 5Mbps upload.

It's hard for me to say exactly, but both upload and download speeds are slower than what the client network is capable of handling. Even tasks like deleting large folders from the server is very cumbersome.

So the network is the problem and not me. It's not a satisfying answer, but oh well. I'm currently using GoodSync to synchronize files to the Samba share, and it is creating new folders. Sending jumps between 50 and 20Kbps. Receiving jumps between 16 and 24Kbps. Is there another protocol that is more efficient than Samba that can be mounted as a network share on Windows?

FTP is no good because I need to retain file timestamps, and apparently whatever server is bundled with OMV does not support that, so it's no good. I have tried FTP though, and it is much faster, so it's really a pity that I cannot use it to serve my needs.