Does your router have webinterface where you can monitor and potentially limit network usage of devices?
I'm not too familiar with the arr stack but if it is constantly downloading videos it's probably using full bandwidth. Maybe you can also limit in the arr settings or throttle the network interface on the laptop.
If you're using QBittorrent, you can throttle upload/download speeds in the settings. I believe it wants speeds set in kibibytes (KiB) so you'll need to convert your megabit internet speeds to your desired kibibyte limit (say maybe 50% or less of your available bandwidth).