You might come to think Elemailer is going to impact the load time of your site frontend in but in general, it doesn’t.
You may not be using Elementor page builder on your site for example and can think since Elemailer requires Elementor it’s going to slow down the load time of my site, but that’s simply not true since Elementor scripts, style sheets, database calls don’t happen on your site on the frontend if you are not using Elementor for any normal page/post. You are in that case using Elementor only for the email templates and to preview them which are separate post types and not your regular WordPress posts and pages hence it doesn’t impact your site’s speed.