BigMinnie how do you measure the load time?
If you're using a tool that waits until everything renders including the iframe, it will definitely increase the time. But the iframe loading shouldn't be blocking. The user should see the base page render and it should be interactive before the iframe is ready. And because the iframe is lower in the page the additional load time for the iframe shouldn't very noticeable by the visitor since they can't see the iframe at first anyway.
Loading the iframe with JS could trick an analytics script into thinking the load time is faster. But in practice I don't think it wouldn't change anything for the visitor. But it could have SEO benefits if that value is indeed used to lower your SEO score.
One benefit of JS+iframe is that we can delay the iframe rendering until it gets into view. This can save up on data usage and server load if you've got many page views but not everyone scrolling to the comments, but won't make things any faster for the visitors who actually scroll to the comments (in fact, the opposite, depending on how late we trigger the loading when the user scrolls).
If there's something slowing down the initial page render of Wordpress, I will definitely fix it. Just let me know which tools return bad scores and I will try to optimize based on their suggestions.
