To save as a Jpeg always use the Jpeg Optimizer.
This handy tool allows you to adjust the compression to achieve the lowest file size without losing definition.

There are two ways to find the Jpeg Optimizer.

Go to "File" > "Export" > "Jpeg Optimizer"


Click the button on the toolbar if you have put it there

Adjust the compression to as high a number as you can without losing definition in the right hand panel