Hello,
the requirement is that domain controllers in which the ADFS Server is joined must be 2008 or later and the minimum DFL is 2003 or higher.
It would be a good idea to migrate your adfs servers after you move to 2016. Here are some migration guides
https://blog.kloud.com.au/2017/02/01/adfs-v-2-0-migration-to-adfs-2016/
Hope that helps
Isaac Oben MCITP:EA, MCSE,MCC <a href="https://www.mcpvirtualbusinesscard.com/VBCServer/4a046848-4b33-4a28-b254-e5b01e29693e/interactivecard"> View my MCP Certifications</a>