Website speed issues are very common, especially in WordPress websites, and can't be resolved easily. I recommend you take the help of an experienced developer who has good knowledge of increasing website speed methods like Content Delivery Network (CDN), use Gzip compression, and browser caching.

Hi, I recommend linking that page with some of those pages that are getting organic traffic, so that the authority can pass, and then try to request indexing in Google Search Console. If it's still not indexed, then delete