Hello,
You can enable/disable Ajax menu loading in Theme Options > Speed optimization. Ajax menu loading speeds up the site loading because it does not load mega menu content from start and loads that only if you hover over the menu. But if your server has a slow response time then it would be better to disable that option to avoid visual issues with the menu. And speed up the server response time.
Could your hosting provider provide detailed reports on what requests cause CPU issues?
Regards