debug an existing wordpress theme

The project consists on helping us delivering a wordpress website that doesn't work properly. It is very slow to render the pages. We have profiled the site, it appears the template we use (WP Residence) is slowing down everything. We can't switch to another template because all the content and design is input already (custom post type, etc). It takes about 30 to 45s to render any pages, which totally unacceptable. It's computing on the server side because since the browser receives the data it is very fast to render the html DOM. We need a wordpress developer having solid debugging strengths in php and capable of debugging WP residence wordpress template. Thanks for your proposals, Olivier