So with my current SD card which I think is old (and possibly counterfeit), my 15 second hyperlase is struggling to finish before running completely out of battery.   I'm assuming this is because it's struggling to write fast enough to continue the 2 second intervals.

So I'm shopping for a proper fast (real) memory card.   

Best Buy has a Sandisk Micro SD Extreme Plus for 34 bucks, and they have a Sandisk Micro SD Extreme Pro for 80 bucks.     Will the plus do or do I need to fork over for the Pro?

Both the SanDisk Extreme Pro and Extreme Plus will work. Or you could use any of these memory cards.

Check out the Samsung EVO cards. $15.50usd They get great reviews.
https://www.amazon.com/Samsung-MicroSD-Adapter-MB-MP64GA-AM/dp/B06XX2GL1L/ref=mp_s_a_1_5?ie=UTF8&qid=1539872897&sr=8-5&pi=AC_SX236_SY340_QL65&keywords=samsung+micro+sd+card+64gb&dpPl=1&dpID=414G05jV6xL&ref=plSrch

Hi NomadRT, thank you for reaching DJI Forum. We do appreciate bringing this query to us. Kindly check the supported SD cards below for your reference. Thank you.