The segment in question is the second climb only, neither noise abatement nor obstacle is an issue here. The 1500 foot altitude was set to standarize operations across the airline's fleets.
According to a performance engineer of the company, the second segment here, ends at 1500 feet and the application of WTAI after 400 ft would definitely affect the 2.4% minimum gradient in case the TOW would be at the maximum permitted under the conditions.
Furthermore, given that the sytems design's objective is to deice rather than anti-ice, I would assume that it would be safe to continue the V2 climb to the acceleration altitude of 1500 feet without the WTAI on and then aplly it after flap retraction is completed and MCT set, as it was supposed to be used and the procedure calls for. The ice accretion would be dealt with at the fourth segment. Is this a sound asumption or not?