The size of the file doesn't matter. Without port forwarding you won't be able to use things like private trackers without running the risk of getting banned. There's no reason to use a VPN without it if your goal is torrenting.
I use AirVPN and it's cheap with port forwarding. Without it, trackers will show you as unconnectable and nobody will be able to download from you unless they've set up port forwarding.
At least one side needs an open port in able to connect. So if your ports are closed, you can only connect to seeds/peers who have an open port. Opening your port ensures you can connect to anyone.
I am seeding 70 torrents on a private tracker, most of it some niche stuff. It's getting downloaded, but I have 0.00 seeded across all 70 torrents. I have no port forwarding.
1 + 1 = you need proton / airvpn.