Something seems wrong with their math. If you reduce the constant by 15% that doesn't mean the whole increases by 15%...no that just means measurement would be lower by 15% meaning the whole would be higher...but not the same amount.
A quick check of the math seems to show in actuality that it is in fact (if the Hubble Constant is 15% smaller than it should be) only 12.75% bigger...
And no I'm not trying to be humorous, just saying they're math sounds a little funny.
Addendum: Now this was REALLY QUICK math on my part and so may be prone to mistakes, but doing the mathematics would indicate I'm on the right track even if I'm not exactly correct (though a quick glance I would say I'm pretty accurate or at least pretty darn close if not spot on).