Thanks for asking. Hope you’re having a great day.
I ran a test on Pingdom and can see an entry for ethos.css. I see that the file is around 26kb. I am sharing the test link URL. https://tools.pingdom.com/#!/ckcdRC/https://www.mkse.com/
I my view, you have the option to keep the website as it is. It seems that you are not using any cache plugins or optimization services on the website. I suggest you to take a look at plugins like W3 total cache and then review our performance optimization guide to further speed up the load time.
On the other hand, please note that you are using quite old version of child theme. You have the option to download and setup the new child theme. And in the same order create the directories and then move ethos.css. You can delete the old child theme after taking a backup. I am sharing the link of child theme that you can use to download. I am also sharing link to the guide that will assist you in setting up the child theme.
Let us know how it goes.