Yeah, bit of both....
Assuring margin for lift capacity enough during turn at a relatively low airspeed. Applies to different aircraft types t (wing planforms etc.) and different additives in airspeed, seems the norm is 10-20kt in this eg. B737 =+15 (less than +15 then a lower bank angle has to be used to not induce to much drag)
As for the increment just for climb (obstacle avoidance etc.) The all engine should give a better climb gradient compared to v2 only... as per briefing notes below...
