Upvote:1
You'll need an eVisa. This is available online, as the name indicates. Fifteen hours is a lot of time to wait in KLIA. You can take the train between the airport and the downtown train station.
If Malaysia Airlines sold you the ticket as is, then they think you can do the connection on the way back. One hour is actually plenty of time, if both flights are in the same terminal (as they should be, since it's all KL).