session variable

Question

I have a question about what is the best way of setting up session variable(s) in the following situation for a change I am making to a C# web form application.
  Currently when the users enter a specfic transaction code that = '123', a property of a textbox is set to visible and the user can enter a comment that is up to 20 characters long.    Now the user want to be able to enter a comment that can be up to 15,000 characters.
  To accomodate this request, I am going to make a change where the user will be pointed to a new web form page where the user can enter the information. Once the user has entered the information, they will click the save button and will be taken back to the orginal screen  they started on.
   **Note: A new web form page is going to be generated since there is not enough room on the orginal page to enter the information.
   When the user clicks the 'save' button and return to the original web page, I am not going to update the database at that time. I want to pass the transaction id (unique identifier) and the new text field that is up to 15,000 characters back to the original web page as session variable(s). Once the user is on the original web page, I will take the session variable that is up to 15,000 characters and update the database in the same manner the database is currently updated.

  Thus can you tell me if using session variables in the case listed abover is a good idea? Why or why not?

  Also if there is a better way to accomplish this goal, can you tell me what the better method would be?