Enough room for 15x10 on a Demon?

Section width. The section width varies per tire manufacturer. If for example you compare section widths and tread widths on a BFG radial T/A 295/50/15 and a Nitto 275/50/15.
Here are the relevent spec comparisons:
BF Goodrich Radial TA 295/50/15
Dia=26.7", Section width=11.8", Tread width=10.4"
Nitto NT555R 275/50/15
Dia=25.7", Section width=11", Tread width= 10"

Take a look at this link:
http://www.forabodiesonly.com/mopar/showthread.php?t=297526

To me it's about how much tread's on the pavement and still fit in there without rubbing.