The first is the limit of the text editing area ... it might be 32k (this is a browser-set limit).
The second is the PHP size limit on acceptable form data. This variable is called post_max_size, see moodle/lib/htaccess for more details.
The embedded editor is not really meant for heavy-duty use - I'd recommend saving the original page as a file and uploading it to the course, or otherwise simply linking to it using a resource type "web page".