Going to need more than that.
If it is local your internet speeds (hopefully*) don't matter in the slightest and your router might be great but if you plugged in a slow cable/device that matters little.
*if it is set up so badly that it is going out into the world and coming back in as effectively external then yeah, though that tends to be something you see right away or you accidentally connected to a guest network.
It will depend what is going on on the server as well. If a lot of people are accessing things, if it is on a slow drive on the server, if the device is having issues with the drive (failing drive sort of thing) and a bunch of other things it could be.
If could be your local machine you are using it on has some form of issue. Hopefully it is also set up correctly (FTP is plain and simple in many ways but in others it shows its age and attendant fiddlyness).
Tests at this point are usually find examples of other FTP servers and connect to them to pull data (or push it). See what goes there.