DFS wrote:

"The cast iron stoves that I'm looking at are running about 15k btu/burner."

15K is pretty low for an outdoor cooker. Most outdoor burners run between
100,000 and 300,000 BTUs. Outdoor propane cookers tend to have larger
burners because folks like to use them for turkey fryers, crab pots,
industrial-sized meals, and cooking in a brisk wind (hurricane). You're not
going to get a 15 gallon pot to boil anytime in the next two days on a 15K
burner.

I'm not going to be the one to give you a stamp of approval to use it
indoors, but I would use a CO detector in the vicinity if you are.