My mongodb total document size is over 16mb

Are you sure you have single documents with a size larger than 16mb? The size limit of 16mb only applies to single documents. The total size of all documents in a collection is unlimited.

In you image, Total Document Size tells you the size of all documents in a given collection. As @Tobias said, limit of 16mb only applies to a single document in a collection. So as long as some document itself does not exceed the 16mb of size, you are good to go.

However, the maximum document size of 16mb applies for BSON-document, and if you want to have documents with more then 16mb of size, you should use GridFS:

GridFS is a specification for storing and retrieving files that exceed the BSON-document size limit of 16 MB.