The rest in the forums are work fine (with speed)
Currently in my list there are 21 addons. 1 Styles.
On a clean xenforo page it was the same where I installed my first plugin.
The number of languages AND the number of styles are a factor (effectively multiply them together to determine the amount of required work at this step). The number of languages is likely a more significant factor actually.
Can having debug turned on slow it down? I swear I have one site that takes a long time too (not 30 minutes though), but the only difference is that I have debug turned on for it.
Debug mode can trigger different code paths and add additional logging, so it's possible (though we do normally disable the logging during this action).