The 2015 Nismo final drive ratio has reportedly jumped up to 3.916. This is up a little from the 2014 Nismo at 3.692 for the 6MT. Assuming the trans ratios are the same, that should make the 6MT a little more... um... squirley.
The 2015 Nismo 7AT appears to be keeping the 3.692.
2015 Nissan 370Z NISMO fast facts - Torque News
2014 Nissan 370Z NISMO specifications