I’ve been doing some more page speed testing with many of the sites I run recently, and it’s an exercise I’d recommend, for a couple of reasons. Firstly, the response time of your site(s) doesn’t stay the same: you may not have added any significant new features to it, but the various resources it uses may have changed. Every time you ‘update’ a plugin, that’s a change of code on your site. Secondly, the speed testing tools are constantly under development, and they can give you different results than last time you tried them.
Google Page Speed Insights is an excellent testing tool which I’ve mentioned before, giving you a score out of 100 and a list of possible technical improvements. One of my sites which I’m sure used to score over 90% there has fallen to 68% recently, which needs some investigating. Mind you, I do tend to fiddle with sites far too often. Other tools to experiment with include GTmetrix and Pingdom. If you’re really keen, keep a spreadsheet of test results so you can check over time that things aren’t getting worse.
You might also like to read How Quickly Should a Page Load in 2020? on Search Engine Journal.