First method is a visual appreciation on speed starting from homepage, category, product page. Make sure you have a good internet connection. Also, depending on browser used, differences can be observed.

Second one, using online testing websites, note that loading speed does not rely only on server speed, indeed the response server time on the market is somewhat misleading, either from google and other online speed testing website... They all include the server speed (in general 20-120ms depending on your distance to server).
We can easily compare on same server the loading speed of a pure PHP website with a prestashop website, we find an uncompressible 400-500 ms difference, even with a top optimized prestashop website, because prestashop for example has to load all modules at first request... and whatever the most server you would use !
Finally, all sites does not load equally, this is simply because each site is uniquely using a custom template, and many third party modules which will all influence the final loading speed...


Test your website on your actual server, move with YOORshop, and test again :
https://gtmetrix.com

Do you know ?

- your ranking in Google will be better if your website loads fast !
- you will sell more on your website because your prospects will appreciate the speed when browsing your catalogue !
- having your website in full SSL is also unavoidable if you want to maximize user experience and your sales :
https://www.yoorshop.fr/knowledgebase/1551/Activate-SSL-for-your-whole-website.html