Sorry for your loss. 15 was a good long life. As the time approached in all my dogs' and cats' lives, it never is easy, and it's still hard to go through, no matter how old they made it to.
I had a very bad year in 2012. My mom died in March at 87. She had wanted to go for at least 7 years. On Nov 12th, my dog Molly had to be put down, she was suddenly unable to walk and her heart was very bad. About an hour after that, I was called by a friend who told me his brother, who I had been friends with for about 50 years, had died. I was generally a mess already, and it really bummed me out. A month and a day after Molly went, her brother, and "boss", King went too. They were almost 14, so it wasn't a shock, but they really deteriorated suddenly. And then about 4 hours after King went, another friend calls me and says, "Guess what I have?" "What?", "Well, I've got liver cancer!". He died in August of 2013, and it wasn't an easy thing for him or his family to go through. hope I never have another year like that.