Tapps PWAs are naturally fast. They display the initial screen and then load the remaining content in background. Also the entire app loads to the user's device for snappy navigation.
Notwithstanding, if you have many big images (1Mb +), then it can slow your app which is not a good user experience.
We automaticaly optimize images used in a call to action because these images are viewed in a small size and are not enlarged, however, we do not optimize Image Actions. If you tap an Image Action, you will see the larger image, which is great on desktop, but has little value on mobile. Thus if your audience is primarily mobile, or if the images do not need to be enlarged, then it is a good idea to optimize the images yourself.
A couple of good options to optimize images are:
You can use these drag and drop applications to reduce a multi Mb image to a few hundred Kb without loosing anything in user experience.