by Visvanath Ratnaweera.
"course completion" is too broad. You need to continue localizing the cause. Have you tried the developer tools in the browser, network tool, for example? It might tell you which part of the page takes long. A brute force approach would be to temporarily activate the DB query log before you click the save button and study the queries Moodle generates.
There must be more methods in the Hardware and performance forum. Check its documentation and run a search in the forum.
P.S. This looks like a topic for the H&W forum. Hint to the mod. ;)
P.S. This looks like a topic for the H&W forum. Hint to the mod. ;)