I'd suggest looking into a download manager that supports resume and multiple download threads (to download multiple sections of a single file in parallel, if the remote server allows it).
First such tool that comes to mind is FlashGet but its years since I last used it, and I don't know anything about the latest version so can't vouch for it.
Maybe check out JDownloader for an open source alternative :
https://jdownloader.org/download/indexOther than that... all that comes to mind is maybe you'd be willing to spend 5-10$ a month on a VPS and set up a VPN or a proxy server on it, and maybe download bigger files on it, then ftp the files to your computer.
If you're in a country they accept, Kimsufi has a promo now with VPSes starting from 1$ a month for the first year ( 1 core, 2 GB ram, 20GB disk space and 100 mbps unmetered, well probably under 1 TB then it's capped at 10mbps for the rest of the month) :
https://www.ovhcloud.com/en/vps/There's tutorials on how to set up a proxy or a ftp server out there, and the specs are enough for that.