No, there's no such option.
If by "renaming every image" you mean renaming the actual files and re-uploading them, you don't have to do that. If you mean editing the already uploaded files, yes you'll have to do it.
The text that shows up upon hover etc. isn't the filename, it's the image title; WP only inserts the filename as a title when you've failed to provide a title yourself.
So, for the images you have already uploaded and inserted, edit each one of your pages, click the Add Media tool, click the Gallery tab; click Show to open each image popup, enter new titles; click Save All Changes when you're done with all the gallery images, click Update (page).
For the pages that are under construction, you can either enter titles after uploading the images and before inserting the gallery, or of course rename the image files before uploading them.