The tentative 2015 Purdue evGrand Prix Rules are now available. The only pending change can be found on page 9 of rules: a switch to 88 volts nominal (100 maximum). Final release should be shortly.
As a reminder, the race will be 50 Laps. The battery capacity (as can be seen in section 2.6.4) of 4,320 Watt-Hours should be plenty sufficient for completing the race.
Current rules for the 2015 race. EVGP Rules 2015 Final