If you are in an area with slow internet speed you can set your Outlook Web App to operate as "Low Bandwidth" version.


Once logged into Office 365, select the Gear icon located top right side of your screen and select Options...

On the left side select General > Outlook on the web version and select the checkbox "Use the light version of Outlook on the web" and select Save. You will have to log out, close and re-open the web browser for changes to take effect.