Ajax response time higher than with CI3

No, I didn't say we should accept any answer, I said we can't compare different things, and I forgot to mention a fundamental fact: CodeIgniter is a PHP framework and the PHP server requirements for each version make them incompatible with each other , if they could run on the same version of PHP it might still be a little fairer, but it still wouldn't be fair, the development of each of the versions was based on what the available versions of PHP offered. Infrastructures are completely different and, normally, it is always necessary to keep in mind the cost/benefit ratio. Greater security and stability weigh on this relationship. Of course this goes for both, the framework and the server, PHP.