If I remember correctly, I think under File Sharing there is a limit of how many queued uploads and how many megabytes of queued uploads per user you can put.
You can reduce both amounts so people can only download a specific number of uploads or s specific number of megabytes at once so your computer doesn't use so many resources.
The other option is to set your folder to private and let people send you a message and ask you if they could download from you. I know some people set it to 2-3 uploads per user and if your internet just struggles to download things they limit the MB.
That's all I remember, sorry if what I'm saying is a bit confusing as my primary language is not English and I haven't used Soulseek in a while!