May 21, 2016 12:53 AM|ManyTitles|LINK
The reason your code is sluggish is because your RAM is taking a hit. You need to create a custom class to read your file. Follow this link
https://siddheshshelke.wordpress.com/2011/10/23/read-large-text-files-using-c/ , it deals with a situation that is exactly like yours.