The ONC has provided a free risk analysis tool. This will be sufficient to satisfy Core 15. Be careful of certain firms who charge from $2,000 as high as $10,000 for solo providers. It is unnecessary.
Here is the download:
http://www.texmed.org/WorkArea/DownloadAsset.aspx?id=25071They basically want documentation of your current setup and what steps you are taking to resolve any potential security holes. The guide will make it easy for you to find out this information. When you're done, print/save the report with the date and file it away safely.