It seems like this would have leaked if Earn.com had earned this much, or if A16Z had earned a large distribution in one year (like last), it would have had to have been reported to their LPs in the net asset value update.
And perhaps it did leak, because we're talking about it. But then I would still guess there would be more discussion about this if an LP leaked it. There would be ample documentation of this.
In June of 2015, the price of BTC was about $240 each.
If we assume half the investment went into bitcoin, it means they acquired $115m/2/($240/BTC) = ~240,000 BTC
At today's price of $8000/BTC, assuming they never sold, those coins would be worth $1.9B. So it is plausible they hold more than $1B in bitcoin.