It is actually likely that won't have enough of her own to actually *maintain* her current lifestyle into the future. Yes, the Hiltons have lots of money, but it is going to be split among ALL the Hilton grandkids (Paris, Nicky, their brothers, her cousins), and it's likely she will no longer be able to live where her family lives now (in the penthouse atop the Waldorf-Astoria) because of the number of kids. All in all, after taxes and if she has more cousins, etc., she may end up with 10 million or less. That is tons of money to most of us, but it won't fund Paris' extravagant lifestyle (jet-setting all around the globe, 10,000 dollar dresses, million-dollar jewelry, homes in multiple locations) in the future. Even if you add in her own earnings from licensing her name, her tv shows and stuff, it's very very likely her lifestyle and spending outpace her earning (as Michael Jackson shows, someone with extravagant taste can easily run through tens of millions or more and end up bankrupt or living on credit to maintain their lifestyle). Also, the stream of income she makes from selling her image/name/rights to her shows will probably dry up or diminish severely in the future--I can't imagine her career being as hot in 15 years as it is now.
Her last two boyfriends, on the other hand, have been billionaires, and it's likely their money will be able to allow her to maintain her lifestyle, or at least come close.