Which plan should I be on?

I’m currently on the ‘Agency’ plan, but since I do not host any sites on Webflow, (I self-host on a reseller account for a web host), do I really need this plan, or could I drop back to a ‘Freelancer’ plan?

The phrase highlighted in blue confuses me. I currently have 15 sites that I maintain, but again, none of them are hosted on Webflow.

You are on the correct plan, with the freelancer plan you could have only 10 sites that are not hosted on Webflow, since you have 15 you must stay on the agency plan