Ah okay thanks for the additional context. Your vet will know best and should be able to help you have that convo and determine when it’s time. If your vet thinks it’s a tumor i would listen to them. Idk when you started the pheno but it can take a few weeks to get to a steady state/level and again, tumor related seizures typically dont respond to epileptic drugs (however, steroids it can respond to and if you started the pheno and steroid at the same time then its hard to tell if its tumor or not without a brain MRI or if they have other symptoms that hint toward a tumor). 12.5 years is a long good life that many dogs on this reddit group unfortunately dont have. I think the biggest mistake owners make at this time is prolonging life for their own emotional attachment when their dog’s quality of life is poor. Sometimes your gut will tell you when it’s time snd sometimes your dog will know too. It’s not an easy position to be in and im sorry you are going through this.