Another factor to consider is the timing of V’s breakfast bolus. People have different digestive rates & timing is important. V can check this by testing at 1 hour after breakfast, as well as at 2 hours & 3 hours.
The 15 carb “rule” is a general guideline. It depends of course on how much BG needs to be raised to reach the target BG. It’s also dependent on what he’s eating for those 15 carbs. Fast acting sugar should be used to correct lows quickly & V needs to know how much fast acting sugar (glucose, dextrose) raises him how many points. Just as an example & I’m a small person, 1 gram of sugar raises my BG 10 points. If I need to correct a low of 50 to get to my target of 90, it would take 4 grams of sugar. People use different things to correct lows (glucose tabs, candy, high sugar drinks, etc). I use jelly beans because 1 jelly bean contains 1 gram of pure sugar. Easy to count, easy to control to prevent overdoing the correction.