If you have remaining funds in your 2015 flexible spending account, AND you will be on the HRA plan in 2016, you may use your Discovery Benefits card for claims incurred through 3/15/2016.
If you are moving to the HSA for 2016, you MUST use up all of your Flex funds by 12/31/15. Failure to empty your Flex funds will result in not being able to use your ACU and personal contributions to your HRA until 4/1/16.