No problem, and adding some more stuff.
Here's a website that has some really good articles on this topic:http://www.pet-loss.net/
The "Defining Quality of Life" article is relevant to your situation, but I recommend reading the other articles too; they're very well-written and helped me sort out my own feelings in the past.
This scale is for calculating whether a pet's quality of life has degraded to the point where it's time to let go:https://my.vetmatrix.com/0033049/storage/app/media/5c2145cb7e460_QualityofLifeScale.pdf
According to google, miniature schnauzers usually live 12-14 years. You said your dog's still only 10, so I'm guessing he may not really show signs and pains associated with old age yet? If the dog's only physical issue is vomiting once a day, the scale in the second link may or may not give him an amount of points that's considered acceptable.
However, if the dog has kept vomiting for that long, I feel like he's probably not going to improve, and clinging to him is just prolonging the inevitable while watching him deteriorate and suffer.
If I were in your situation and hesitant to make the decision without a noticeable sign, I'd probably do it something like this; if the dog vomits X amounts of times in Y amount of time (you can decide together with your wife how often is too much), it's time.