The 15 kW is a bit of a surprise to me as this conflicts with numbers given by Holmlid's paper "Existing Source for Muon-Catalyzed Nuclear Fusion Can Give Megawatt Thermal Fusion Generator".
For comparison: the central gas heater in my Dutch home has a nominal power output of 22 kW.
Looks like they did not want to include power caused by meson decay although this design includes a 'muon thermalizer'.
This does not look like a wise promotion.
That paper mentions too a starting 15 kW output power, excluding the energy from the initial mesons (eq. 5, section V).
But then Holmlid also states that the power of the decay of the initial mesons would be 220 kW (eq. 7), which on a first sight doesn't make the complications from having to deal with tritium to reach higher outputs (slowly over time) very attractive. Also, protium (ordinary hydrogen) would work too, as even the latest paper on the interstellar rocket points out.
...unless producing tritium in large amounts is actually the point.