Remember, one day at a time. Do you track your calories? Maybe plan ahead for the day this way you know exactly what you can eat and what not to go over.
go for a walk, pop in an exercise dvd or pull out the wii fit, just get moving!
15 lbs is no fun, but at least you didn't gain it all back, I gained back 10 and am now only 4 lbs away from being back at a -40 lb loss, I can do it, so can you!