Calculating temperature increase is directly related to the power input.  All of the power input by any mixer is converted to heat.  A rough calculation for two 15-inch disperser blades looks as if you could put most, if not all, of the 15 hp from the motor into the batch.  The 15 hp represents 42 Btu/min/hp for a maximum input of 630 Btu/min.  The calculation for 35,000 cps predicts more than 15 hp for two disperser blades, but the material is likely to thin even more at the 475 rpm.  Your tank should hold about 535 gal or 4,500 lbs of material.  Assuming the contents are water based, you can use a heat capacity of 1 Btu/lb-degrees F.  If you figure that you are adding 630 Btu/min to 4,500 lbs of 1 Btu/lb-degrees F material you will get a heating rate of 0.14 degrees F per minute.  Obviously, running for 10 minutes, the temperature will rise about 1.4 degrees F from just the disperser.  You must then add the amount power input by the helical sweep impeller.  If you use the total horsepower of both motors, you will get a maximum heat input.  Staying below 80 degrees F will depend on how much total power you put into your batch and how long you run the mixers.