It was first revealed back in July that The Undertaker would be working the 2015 WWE tour of Mexico, which just wrapped this past weekend. As noted, Taker teamed with Kane to face Luke Harper and Braun Strowman on three shows in Merida, Mexico City and Monterrey.
One of the main reasons WWE put The Undertaker and Ric Flair on those shows is because of heat from Mexican promoters Ocesa, according to a well-placed WWE source.
The promoters in Mexico were having major problems with WWE over how WWE first sold them the shows and then did not book any top talents or any real Mexican stars, as they don't have any really. When WWE books a tour like this, they sell the tour to local promoters and receive a certain amount of money in return. The promoter then has to sell tickets and make a profit, hoping that what WWE has sold them will really draw in fans. WWE also receives a percentage of money over a certain amount.
The promoters of the Mexico tour had pulled all support until WWE promised to book a big name, which is the main reason why The Undertaker was added.