Well, I panicked after the two seizures in four hours on June 15, and went back to 15 mg bid.
Milk's been back on that dosage for a while now, and it seems to be having a much less negative effect on him than the last time. He's not sleeping as much, he's cuddling again with the other cats, and he is just generally "here" again. And he's much more interested in food this time, thank goodness. There have been no seizures since the dosage increase. I still have the 10mg vet chews, and at some point, I'd like to try to reduce the amount of phenobarb again, but maybe it'd be a good idea to wait until the next time his blood levels are checked. I'm hesitant to do anything to rock the boat again.
One small thing I've noticed - twice in the last few days (the second time was tonight), Milk was sleeping on the back of the couch, and he fell off. The first time, he went forward and landed in one of the kitty pi's, looking like he'd been sitting there all night. Tonight, he fell backward and ended up sitting up on the floor. He appeared a little dazed. There was no meowing or foaming or anything else that happens with a regular seizure, so maybe this was a petit mal seizure, or maybe it wasn't a seizure at all? Although, I've never seen him or any cat fall off the couch in their sleep. Something to keep track of, I guess.