Optimizing self-hosted gitlab performance

Hi, I hope this is the right place to post this.

I am using omnibus gitlab v15.8.0.

Since upgrade from v13 to v15, frontend loading times have become noticeably slower.
It seems to me that the first and second page loads are always slow, and then some form of caching kicks in and the subsequent refreshes are much faster. I cannot find any settings related to cache so that I could tweak it - maybe increase the cache size and keep the files cached for longer.

I’ve also opened the performance overlay to try and analyze the loading times. I can see that .png and .ico loading times are really high. Is this normal, can I do anything to speed this up?

I’ve tried adding CPU cores, adding more puma workers and assign extra memory to them and adding more sidekiq workers. postgresql, gitaly and redis all seem to be working OK (20ms - 60ms response times, according to the performance overlay).

Can anyone point me in any direction? Am I missing something? Any and all comments appreciated. Thank you!