for being in Texas 215 is not hot....I ran my 400 for almost 10 years here (25 k miles) and running it at 205-210-215 in summers (June -Sept)it would run about 195 in the rest of the year....this is hwy speeds at 70-75-80.
this year , getting ready for the Cannonbird Run, I changed my radiator to an aluminum large 3 core and it brought it down 15-20F.

but as for "hot" 215 here in Texas isnt running hot...
test it some more, run it longer at speed see how it reacts....when I first bought mine and drove it back from Dallas on a hot August day it ran 225-235 all the way, 240 uphills. I found it was missing the X fillers, and one side missing of the lower rubber/masticated radiator fillers, plus prev owner had added a push helper fan that was blocking air. just those 3 things brought it to run better/cooler.

timing, and if it runs too lean can also bring temps up.

and running with no t-stat is not good, the t -stat needs to be in there to slow the water down ,otherwise it wont have time to cool down in the radiator....