I recommend maxing out the manual stat to make this a lot easier for you.
All I did for this was start a manual at a low or no speed so you don't have to worry about avoiding obstacles, and just jump and manual again. The first few, you can do in rapid succession. After about 7-8 of them, I would recommend trying to balance back to the center of the meter before jumping so you're not starting your next manual toward the ends. If you don't do any other tricks, the multiplier for your combo will be a clear indication of when you hit 15 manuals, and you can land the combo.