I checked you site in GTMetrix and the issues are not related to the theme but your overall WordPress setup. See the GTMetrix result in the secure note.
Regarding the Reduce the number of DOM elements, you have too many contents in your page, you must break your page down to separate pages.
I'd also recommend that you review our Performance guide at https://theme.co/apex/forum/t/customizations-performance/210
Performance optimization is a wide area and involves things beyond the theme. Therefore, please note the disclaimer in the performance guide: