Yea, 10 minutes of flight time seem incredibly high to me. That means you could significantly increase it with external fuel tanks (say, for a total of 20 gallons). 15 minutes would be a darn long jet pack ride. Limiting factor is actually just how much weight you could plausibly carry on your back.
it seems they are using pure jets and in this case high-by-pass would be a way to immediately improve the thrust and thus to decrease the fuel consumption.
(Edited numbers.)