More or less every theme produced by wp is heavy loading these days. I don't know from where you have gotten a simple looking theme but if its simplest then it maybe also not mobile optimized fully. Have you checked that?
And I am assuming that you are not using any unnecessary plugins and what nots. So, check the page-speed insight itself. It itself shows a detailed analysis on what factors your page is failing.
And I am assuming that you are not using any unnecessary plugins and what nots. So, check the page-speed insight itself. It itself shows a detailed analysis on what factors your page is failing.