That first part is a bit vague don't you think? You need to define exactly what "having feelings" really means because if it's simply reacting to stimuli, plants do that.If the world was turned upside down and all the scientific evidence was proven to be wrong and I was proven to be a schizophrenic who was only imagining what I saw through my own eyes and animals were actually inanimate objects with absolutely no feelings, then that might change my mind, but I would still eat vegan food to be safe - also because it tastes way better and is better for me as well.
If your answer involves having a nervous system you need again to think about what that means. Nerve cells are just a specialized kind of cell adapted to a particular purpose, they are different from other cells only in degree, they aren't magical.
The dichotomy animate/inanimate is not scientific. From the point of view of science life is a chemical reaction like any other, just more elaborate. Instead of thinking of animals as special and rocks as 'just inanimate matter' a more realistic view is to see the continuity and the wonder of the material universe in which animate and inanimate are part of an unbroken spectrum.
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It's a complex bit of math to work out exactly and requires some information I don't have but if it is longer it's not much longer except perhaps in the case of cows. In any case the downside of the slightly longer average lifespan is instead of being knocked on the head and killed instantly you either get torn to pieces and eaten alive, die of disease or slowly of starvation.the natural lifespan of livestock is on average much longer than their lifespan in farms.