MiTu, the Latino-oriented online-video network, said it has raised 50 percent more than it initially had announced in a Series B round that now totals $15 million.

The company also announced the hiring of Martha E. Flores as Chief Editorial Officer and Greg Griffin as Head of Product Development. They will head major expansions of MiTu’s editorial and product-development operations to be financed by the new round.

The raise was led by Upfront Ventures of Los Angeles, with new investors AMC Networks, Daher Capital and Northgate Ventures, along with additional investment from many of the site’s previous investors. Upfront has been a big investor in several Los Angeles online-video operations, including Maker Studios and Epoxy, which announced a string of deals yesterday. Other previous investors include Machinima founder and Chairman Allen DeBevoise, The Chernin Group and Shari Redstone’s Advancit Capital.

“As many of the big media companies have swallowed up MCNs, it’s great to see MiTú become one of the largest independent online video producers” said Upfront’s Mark Suster. ” MiTú is dominating the fastest growing, most politically important demographic group in the US – Latinos.”

The three-year-old MiTu is the biggest Spanish-language multi-channel network on YouTube, representing 1,300 channels with 12 billion total views. It has studio operations in Culver City and in Baja California, and deals with Maker, Televisa, Discovery Familia and other outlets.

MiTu also has a smaller operation focused on Portuguese-language programming targeting the huge Brazilian market and beyond. In recent times, the company has been creating more Latino-culture programming for bilingual or English-only speakers.

The oversubscribed round is a big win for founders Beatriz Acevedo, Doug Greiff and Roy Burstin, who is CEO. Acevedo told me in December that the company had been repeatedly approached by investors wanting to buy all of it, much as many other large MCNs have been scooped over the past year or so.

Acevedo said then the company wanted to remain independent for the foreseeable future, but that the new funding will position it to compete strongly in the fast-changing online-video marketplace.

As for the new hires, Flores was previously VP of Editorial at Demand Media, and also has worked at US Weekly and the Los Angeles Times, where she was part of the staff that won a Pulitzer Prize for its coverage of the 2003 Southern California wild fires.

Griffin is also a Demand Media veteran, working there as its first VP of Product. He also was Head of Product for Spiritclips, a part of Hallmark.