How to Store text of 15 to 20 KB file data in blob or as text?
If it's the textual content of the files you are concerned with and you need to search that content, store it as [n]varvchar(max) and consider using a full-text index on the column.

If the files are XML, consider storing the content using the xml data type.

If the files are some format other than plain text and you want to preserve that format, use BLOB storage. For SQL Server Server 2012 or newer, you can use FileTables.