Wordpress upgrade: Faster embedding option or a plugin

At the moment the wordpress iframe shortcode is terribly slow and there's no way around it for us Wordpress users. Since using a subdomain would affect the avg. session duration and also negativly impact the seo there are basically only bad options for us Wordpress users. Options are pretty much: a) embed the iframe (which loading speed is so slow that it will have customers leaving the website) or b) use a subdomain that would negatively affect the seo and isn't just either a good user experience when the theme/layout switches. For me this is turning out to be a dealbreaker, since seo and google rankings are so important. I hope you guys find a better solution asap since everything about Twice is great otherwise, and I would really like to stick with it.