Hilton Worldwide Holdings and other big hotel companies are intensifying efforts to recruit properties from competing brands, a way to maintain growth as new hotel construction slows. Spark by Hilton is the company’s 19th brand, but it is the first one that was built to be a pure conversion vehicle with a consistent look and design at every property. The brand is aimed primarily at bringing independent and rival properties into the Hilton system, said Matt Schuyler, chief brand officer for Hilton.