I moved to a place with fiber internet, but FileZilla downloads seem even slower.

[3s34rtfvFQErvb]

First I have little to no knowledge/experience in this stuff. But I know I've used FileZilla for a while, and right now I've been downloading a 5gb file at only half done with 27 minutes left.

I used to live somewhere with slower internet that was faster than my current incredibly fast internet.

What can I do?

[botg]

What's the latency to the server, especially during ongoing transfers?

[3s34rtfvFQErvb]

Don't know how to do that. Googled it, this? https://ftptest.net/

I type user name and password but I don't know the port number. And it tells me this after:

Error: Server refused FTP over TLS

Make sure your server allows FTP over TLS and has a valid certificate configured.
Some stateful firewalls filter the AUTH command. If that should be the case, replace the faulty firewall.

[boco]

Determining latency is done by pinging the server while a transfer is in progress, and measuring the roundtrip time (that's the "time=" value).

ftptest.net is just for checking if the FTP server works in general. Should your server not support FTP over TLS, you need to switch the profile to "Plain FTP" beforehand.