WordPress is too heavy for my small instance. In particularly Admin pages is heavy. Pages viewers is not really because of page caches. (These pages are heavy too when not on caches.)
However, I found a web page about WordPress running time. I installed a plugin “001 Prime Strategy Translate Accelerator” which introduces in the page then my WordPress web site improved a little bit. This plugin improve performance with MO files (translation files) caches.
I am using W3 total cache for overall performance. Some blogs say it is good for admin pages performance to disable Object Cache of W3 total cache. ( ((Japanese) WordPressの管理画面が重い場合の対処法) ) I did it. But I don’t know how good it is.
Some people might say anyone would not care about performance of admin pages. But I do. Because it makes me very frustrating. I gave up writing posts many times because of it.