Opera browser slow stream on YT

Hi guys,
I have been having an issue lately. My main browser is Opera and I also use the default VPN. When I watch YT the videos have issues loading the clips even in 144p. I know that VPN slows the connection but the same video in Opera browser on linux Mint streams in 720p in the same conditions. Firefox seems ok but Opera is somehow terribly slow even without the VPN. I was shocked when I was tethering internet from a 4G mobile phone and the streams had 320p which was more than from my 55Mbps fibre broadband. Seems that the open source realtek driver has an issue with Opera. Anyone having the issues?? THX