Wood in it's core wouldn't reach the 150C you are saying, but would achieve critical temperatures. That's the point I'm making. When you pull the parts from the wax, there would be residual heat that would then continue to cook the spores.
Given a certain amount of pressure, 5 or 6 lbs, the temperatures of the steam could be increased. I don't have any math about it, but I have been watching the "Engles Coach Shop" channel on YouTube, where in this video he talks about Steam bending wood.
At the time point in this 20 minute video, he mentions using pressure to increase the heat of the steam. The critical points are at 10:50, and 13:20. Of course, you can't boil water hotter than 212F (100C) unless you increase the pressure, and he kind of gets it backwards, but I understood what he's saying...
https://youtu.be/1pPKUgpn0CI?t=650Using Tim Rowe's method, the wax would be rendered, the chamber closed, and pressure allowed to increase to the 4 to 8 lbs needed to increase the heat of the steam.
===================================
All that being academic. I don't see why there would be an advantage to a spore to tolerate temperatures greater than the usual living environment. The bacteria isn't an Alien from some dystopian civilization in deep space, it's an opportunistic disease on Earth. You and I wouldn't be able to tolerate temperatures higher than 140F degrees for any length of time, our proteins would coagulate like egg albumen in a frying pan.
Spores are meant to allow seeding after extremes, so they are tougher for whatever purpose, but not impervious. It's been said it the spores can be destroyed at a temperature of 300F (150C) for 10 minutes. If the temperatures can be held at a lower level for longer time, I can easily imagine it would have the same effect.