Epic Games Inc., the creator of the smash-hit videogame “Fortnite,” is valued at almost $15 billion as part of a major new investment round, according to people familiar with the matter.

The company on Friday announced investors have purchased $1.25 billion in stock. People familiar with the matter said not all of the money is going directly to the company. A portion of that amount represents shares being sold by existing stakeholders who are cashing out some of their investment.

Epic...