I like to do this job.
I'll use advance technologies like, PHP, MySqli, HTML5, CSS3, Jquery, JSON, Ajax, and Bootstrap, as per required to fix your wp menu issue.
I'll optimize your site css, js and images.
I'll install and configure cache plugin and image opt plugin.
I'll try to reduce server response time if possible.
I'll give you 2 weeks free support in regards of this project
so let start discussion and start project, and thank you for reading