Halo: Forward Unto Dawn actress Jenna Berman, who played Kelly, has reportedly been cast to reprise the role in Halo 5.
Berman's IMDB profile lists her involvement with the project while the game's page also mentions her as taking on the role of Kelly-087.
IMDB can be edited by anyone but isn't fact checked like Wikipedia so it's probably best not to take this too seriously but Reddit seems to have a lot of love for the idea of Spatan IIs making a return in Halo 5 and presumably the wider Halo community as well.
The site lists Steve Downes as once again filling Master Chief's shoes, Tony Giroux as Fred-104, and Keith Szarabajka as the Didact though in this case IMDB actually notes that his involvement is a rumor.
Not much is known about Halo 5 with Microsoft reluctant to even officially name the game which newly appointed head-of-Xbox Phil Spencer has said will be "legitimate". Spencer has also commented that developer 343 Industries has "a great plan" for Halo at E3. There have been persistent reports that Halo 5 has been pushed back to 2015 with Halo 2: Anniversary slated to take its place this November.
The game, whenever it arrives, will be the second part of the Reclaimer Saga which began with Halo 4 as a planned trilogy but has since expanded in scope.