Hi @Aigle, thank you for reaching out. If Opera is being picked up by CCleaner, it will mean that it is either on the computer, though not in use or that it was historically on there and there are some file remnants left over after uninstallation.
With regard to the decrease in speed, is this when you are using the Private Connection? Your internet speed will generally decrease somewhat when using VPN technology as it needs to go through an additional server.