Hi,
Such issues will only happen while you're tweaking the settings of the website. I would recommend to turn off caching mechanism while you're building your website and activate them back once you have the settings figured out. That will avoid a lot of hassle wondering why your changes are not taken into account when they should.
Regarding the caching on Joomla, the standard settings of Joomla can already do a lot and otherwise, Varnish is also compatible with HikaShop.
Also, using PHP 7, like you already do, is also great to speed things up.