Performance of opening a file added in the project.

In our project we have created an extension so that we can add  Algol and COBOL file to the visual studio and run it. 

We are facing performance issue. Opening a large file added in the project  takes more time than opening a c# file of same size in the console application. There is difference of 7 seconds. 

I don't know where is time going. i have debug and get to know that about 99 percent of the time is taken by a method OpenStandardEditor() which is of visual studio.

Why this method is taking more time in our project.?

Is this due to the different extension for Algol and COBOL files?