If one has the skill to execute a go-around OEI from "over the fence" at Vref +15 with no flap, why would one be 15 knots too fast in the first place?
Easily happen when teaching students on their initial light twin. Gust factors, ham-fisted flying, you name it. After all, it is common knowledge (and this is from personal experience) to see airline aircraft at the flare 15 knots or more too fast beyond the published VREF.
However, back to the point made by the OP and that is the nomination of one arbitrary or generic 'committal" height during a single engine approach below which the pilot is supposed to, if necessary, commit himself to a forced landing or prang on the runway rather than risk a go-around. 400 feet seems to be a favoured figure used in initial twin training schools. IMC go-arounds from an instrument approach are a different matter altogether and responders are right in that a calculated MDA is a wise move in the pre-planning of the approach.
Instructors have a responsibility to teach their initial twin candidates a realistic altitude on short final below which a single engine go-around becomes a marginal manoeuvre. It is good instructional technique to start off by undertaking single engine go-around training at a safe initial height in a training area. Use 1000 feet above ground level as a simulated airfield level. A series of go-arounds can be practiced at various altitudes, to include demonstrations by the instructor. Repeat until the student is competent. That way, time is not wasted in the circuit area. The same technique should be taught "under the hood" until the student is confident, competent and knowledgeable of all the factors involved.