The payout has increased due to strong ticket sales over the past two days, said Texas Lottery Commission spokeswoman Kelly Cripe.
The Powerball lottery draw will be held tonight. The game is played in 44 states, Washington DC and two US territories — Puerto Rico and the US Virgin Islands.
The jackpot is worth $930m if a winner chooses an immediate cash payout instead of annual payments over 29 years, according to the Multi-State Lottery Association.
The grand prize in tonight’s draw is the world’s richest lottery jackpot that could go to a single ticketholder, and the amount is expected to rise further before then.
The Powerball jackpot has been growing ever since the last winner was drawn in November.
While the current $1.5bn prize is by far the largest ever up for grabs in North America, Spain’s El Gordo lottery, or ‘the Fat One’, had a prize pool of $2.45bn in December 2015. A year earlier, it totaled $2.7bn.
However, El Gordo payouts are awarded to thousands of ticketholders while Powerball’s riches could go to a single ticketholder.