So you would choose to live a happy 15 years and then die. Unfortunately most animals that we farm cannot and do not live happy lives, and they don't get a choice. You would more realistically be living to 15 until slaughter with torture, rape, and your children being taken away to further the cycle. Never existing seems better. There is another option though, not raping, torturing, and slaughtering for humans to consume. Humans won't wither away without animal products.
In the not so distant past slaves were given "happy" lives by there owners. They were lesser beings so they should be happy to be alive at all right?