Index: editor-style.css
--- wp-content\themes\twentyfifteen\css\editor-style.css Base (BASE)
+++ wp-content\themes\twentyfifteen\css\editor-style.css Locally Modified (Based On LOCAL)
@@ -24,7 +24,7 @@
 
 body {
 	color: #333;
-	font-family: "Noto Serif", serif;
+	font-family: "Noto Serif", serif !important;
 	font-weight: 400;
 	font-size: 17px;
 	line-height: 1.6471;