Probably quite difficult. That said, miles probably don't mean what you think they mean. United has three categories of air miles:
- Lifetime flight miles are the total number of miles that you've flown. These count towards your million mile status (when you get enough in this category, you get status for life).
- Premiere qualifying miles. These are the number of miles that you've flow, with a few small tweaks, which count towards your premiere status for the next year (25K for silver, 50K for gold, and so on).
- Award miles. These expire if you don't fly with them for a while (18 months, I think), accumulate roughly in proportion to the number of dollars you spend with them (with a multiplier for your premiere status) and can be used to buy flights, upgrades, and so on.
I believe that this person was given 15 million award miles. That doesn't mean that he can use them to fly a million miles. For example, a transatlantic flight (around 2.5-6K miles, depending on the route) booked with award miles costs either 30K or 60K (depending on whether you want a guaranteed flight or a chance to be bumped). And you still need to pay airport taxes for the trip (likely around $100-150). If you want to upgrade to business class, I think it's another 20K miles and a $500 fee.
That said, 15M award miles is probably enough that he'd never need to pay full price for a flight ever again. It's enough for 125 transatlantic round trips, which is a lot more than most people take in a lifetime (though some people obviously do: you can spend all of those miles without reaching million miler status).
They've definitely changed the way they allow you to use miles. I splurged on a 3 person trip to Europe, first class, and it cost me about $120 per person and around 300,000 miles total. That was in 2013. I was thinking about going to Australia for New Years and they wand 180,000 miles + $40 round trip in coach to Sydney. That's per person. The taxes and fees are surprisingly low but the mile cost is high. That being said, I had thought about going to Copenhagen with less than a month's notice and there was (surprisingly) a ton of reward seats left on the flight. $60 in taxes and 40k miles. I still haven't quite figured out how they value the miles now. It used to be a flat rate - 25k for domestic and 55k for international - assuming you got a reward seat and not a normal seat.
As for all the hate on United... well I think their service is definitely better in 2016 than it has been in the past and I get a free upgrade to economy plus at booking. I get upgraded to first class around 30-40% of the time so I am happy to stick with them even.