Nexage added $5 million to its second round of funding for its real-time bidding platform for mobile ads today, bringing its total Series B to $15 million.

Publishers and developers can use Nexage’s system to reach “high-value” consumers in order to increase revenue and engagement.

With so much discussion occurring in the industry about mobile monetization and the growing interest of targeted, real-time advertising, Nexage seeks to capitalize on a massive marketplace. According to Gartner, the mobile advertising market is expected to grow to $20.6 billion by 2015 and mobile RTB will constitute 30% of the market.

The initial $10 million came in on June 6th and was led by SingTel Innov8. The additional chunk of change was invested by Hearst Ventures, the center capital arm of Hearst Interactive Media.

Hearst also joins Relay Ventures and GrandBanks, who previously invested in Nexage’s first $4 million round in 2009.