I am aware that VPN may slow down internet connection , however I don't use it at all.
About opera://flags, it open very quick. Refresh also open that page immediately.
My network is very stable because I use cable.
There must be typically opera reason why it loads webpages so slow as I mentioned before: edge, chrome works just great. It's opera specific case and I really can't find the reason. I woudn't abandon that webbrower because I really like it and it's very useful for me but at the moment because of the loading time it's not comfortable to use.
Maybe my cpu is too poor ? I got intel i5 2400.