A lot of the transmission to engine temp correlation, depends on the trans cooler type and location.
My Freightliner chassis , uses only a trans fluid to engine coolant , heat ex-changer in the lower rad hose , so the trans temp is consistently cooler than engine temp , because the cooled water from the rad , cools the trans fluid , before it goes back to the motor. So knowing your trans cooler type and location is important to figuring the temp range that would be normal for your rig.
Some where I have info on , trans temp , that would be considered detrimental to the trans fluid and internal components , as soon as I find it , I'll re-post.
JMHO: 215 degrees is not a problem. But I'll confirm.