Upping the rpm with a downshift is your best defense given it powers the fan faster and moves more fluid through the radiator and heat exchangers. Don't be concerned about using the down arrow on the shift pad to keep the rpm up while climbing.
215F and some peaks a bit higher would be well within the allowed heat tolerance for Transynd TES295 fluid. It is time/miles at temp that is the issue. So if you run 225F 2% of the time while climbing and 210F or less 98% of the time the 225F has very little influence in the life of the fluid. Fluid analysis once a year would set your minds at ease.
Transynd has far better heat tolerance then Dexron and these are the temp vs life expectancy numbers in miles for Dexron.
175 100,000
195 50,000
212 25,000
235 12,000
255 6,000
275 3,000
295 1,500
315 750
335 325
355 160
375 80
390 40
415 Less then 30 Min.
I think each coach is a little different and if yours runs 215F but that is normal for your coach then do not worry about it. Keep the radiator clean, rpm up if climbing, and if you get concerned have a fluid sample pulled at some frequency to see where it stands. More than likely it will be just fine with the kind of service our RVs see.
Later Ed