Opera can be configured to start with multiple homepages, but this type of setup has a major drawback — opening multiple webpages at the same time may slow down your browser's operation. Fortunately, Opera offers a simple way to remedy this issue.
How To Stop Opera from Loading Background Tabs
Click on the Opera > Settings > Browser > Advanced settings and then tick the Show advanced settings checkbox:
Go to the On startup section and then tick the Delay loading of background tabs checkbox:
While setting is enabled, Opera won’t load background tabs unless you click on them.