Well, that would make it something like a 215/70/15. No wonder you could spin the wheels!
Those tires would have a contact patch of about 26 sq. in. Mikes 255/60/15 have a contact patch of about 37 sq. in.
If you apply 100 lb-ft of torque to each, you were applying 3.9 lb-ft per sq. in. and Mike is only applying 2.7 lb-ft per sq. in. That’s only 62% of the same torque per sq. in.
Add in the difference in tire diameter (26” vs 29”) and the difference in rear ratio (3.23 vs 3.73) and you were easily applying more than double the torque to the contact patch.