@Vaidas: We have a testing environment but it is not usable in cases of implementation of optimization. It's basically what Rufus Rugi said: the problem is that the testing environment doesn't have the user input load, as well as other things that only run on the live site. Yes, we can test only if something works without breaking when run for the first time, but we cannot test properly if it will have a positive effect on execution times.
@Evaristo: We can't do this as Sakiz105 already noted, because we'd have to give access to our proprietary code to strangers without having a non disclosure agreement signed. There's also an issue of trust that we have to have that the person with access won't unintentionally or intentionally do a lot of harm. Also, problems on systems like these require people to examine the whole codebase, which can take weeks, and I doubt even the most benevolent coders are prepared to work that long for free.
@EGM-Manon: Sorry for reopening the thread, I just wanted to add my last word.