If you need a V2+15 climb, then you don't engage the automatics! Seriously though, to get into the accel mode, we would press VNAV. This reduces to climb power, and starts the acceleration. If you just want to climb, then at 1500' pressing N1 on the mode control panel engages climb thrust, and the flight director/autopilot will maintain V2+15 (about) until 3000' when you engage VNAV to start accel. Most of these procedures were designed (I think) for Chapter II aircraft, which will be gone soon!