Hi,
Note that even if you disable the Falang component, if you have the Falang system plugin enabled, it won't change anything on the frontend. The plugin, which handles Falang translations on the frontend, will still run normally. So if you want to disable Falang, you also need to disable that plugin.
And Falang is quite resource hungry as it needs to run an extra MySQL query for (almost) each query your website runs without it. And on top of that, it needs to process the queries and the results of those queries to replace the texts with their translated texts.
HikaShop's translation system doesn't add much extra processing. It relies on the Joomla translation overrides system. So when you use it, it just increases the size of the language override file where the translation overrides are stored. But processing a translation file, even if it's big, is not a problem. Joomla and PHP are optimized as much as possible for this since Joomla already needs to parse dozens of translation files for each page.
So if you have resource issues with Falang, migrating to HikaShop's built in translation system would solve the problem. However, that also means having to add back all the translations as there is no tool to automate the migration process as far as I know.