Since 2013, several launches up to the ISS have taken a fast-launch. First initiated by Soyuz TMA-08M, the fast rendezvous takes the crew up in 6 hours where the previous time-to-dock was around 2 days.
Obviously the human body is capable of surviving the acceleration/deceleration involved, and contemporary technology capable of the precision required in docking - cutting down time from 2D to 6H. Yet (please correct me if my assumption is misfounded) How long does it take to get to ISS? indicates the quantum of time to get to orbit itself is only a small fraction of the total time to rendezvous - and the time to orbit has not changed significantly over the years. From reading various reports available on the internet (e.g. STS reports) my take is time-to-orbit has consumed 30 to 40 minutes - and continues to do about the same.
Technology allows us to cut-down on time-to-rendezvous from 2D to 6H around 80% quicker. Say a mission does not need to get to ISS - it is only up-around-down; how much can the time to orbit from launch be reduced?
Apart from the physiological constraints on acceleration, and hardware -how much quicker can we get to orbit from launch? Can the time to orbit at-least be halved from approximately 30m to 15m?