I'd just like to make a couple of points,
1. The increased V2 climb technique is used to maximise the performance of the aircraft when the climb limited mass is more restrictive than the field length limited mass, using an inceased V2 will allow an increase in Take Off mass and the aircraft will still meet the field length limited mass requirements (as speed increases you get closer to Vmd which is where Thrust minus Drag is a maximum and therefore gives you Vx the best gradient of climb speed). Whatever happens you must still meet the JAR min requirements of 2.4%(2 eng) or 3.0(4 eng)
2. As to the question of 15 feet screen heights vice 35 feet screen heights in wet conditions it is full explained in JAR 25 AMJ25X1591 this reads as
".....for 1 engine inoperative.....the take off distance required on a wet runway is the distance from brakes release point to the point at which the aeroplane is 15 feet above the runway, consistent with the achievement of V2 before reaching 35 feet, assuming the critical engine fails at Vef corresponding to Vgo(V1) for all the rest of the wet runway requirements with all engines operating the aircraft must meet the 35 feet screen height....."
That is all theoretical and in the JAR, what really matters is flying safe and not taking chances, don't let companies push you to ignore performance calculations for an extra 2 tonnes of freight for the bosses to drink more champers on the back of overworked and underpaid crews