We have a busy website where we never used SSL. Recently its indexed by Google as https://www.example.com.  The users are getting security certificate errors. In google webmaster tools we can only remove the relative URL. For example, any thing after http://www.example.com. I am using IIS 6.0 to host the site .net website. I have seen similar posts here and there and almost all of them recommend a redirect. I don't want to set up a redirect as it will slow down the site loading. I guess I would also need to setup a new website on IIS  with HTTPS protocol and then do the redirect to HTTP site?
Remove HTTPS site from Google search index because users are getting a certificate error
google search console;web hosting;https;google index;iis