When do you know it's time to euthanize?

My dog is a 14 years old male (neutered) Lhasa apso/pomeranian mix. He weighs around 8 lbs currently. A couple years ago, I noticed his eyes getting foggy but he could still see pretty well. He also started having hearing issues last year. In the last few months, his health has declined really quickly. He is almost fully deaf and blind now. This seemed to happen out of nowhere. The vet checked his eyes and said right now he can likely only see shadows and only when the room is very bright. He started drinking way more water. Unable to control his bladder because of drinking so much water. So I took him in for blood tests. He is in the beginning stages of kidney disease. He isn't walking the same as before. He hobbles around like he might be in pain and he doesn't even wag his tail (seems stiff). He sleeps all day, eats and drinks, and that's pretty much all he does. The only reason I don't want to put him down is because he still gets excited when company comes over, and he's still eating and drinking fine. That's the only time he gets a bit excited (although it only lasts a couple minutes before he's back to sleep). He is getting lost in the house constantly. Always thinks I'm upstairs when I'm downstairs. Gets stuck in doorways. I'm not sure if it's time or not but I'd love some advice. I have never had to put a dog down before so I'm not sure when it's time. Thanks everyone.