The question of how many generations is moot; evolution is not a destination. If they survive, they survive. But what do they do to survive? And how does this affect the direction of their evolution over time? Before evolution can begin, natural selection of both individuals and cultural practices will be at play.
The first few weeks would be sheer hell for these unlucky transported souls. The change in gravity wouldn't kill them instantly, but would wear them down, hour-by-hour, day-by-day.
It would be hard on their hearts and circulatory systems. Their blood would weigh 50% more than on Earth, so their hearts would have to work 50% harder to push it around. The elasticity of their blood vessels would be put to the test. Varicose veins would abound. Many would perish by hemorrhagic stroke, and many more would be sporting blotchy, red skin. Feet would swell. Breathing would be difficult, as their diaphragms would have to push up against air and lungs that are now 50% heavier. Blood/oxygen levels would be lower than normal. Fainting and passing out would be common, and would often be deadly; they'd hit the ground with 50% more force. On top of this, their Earth-acquired reflexes and coordination would be hopelessly out of kilter. Bones would be broken, joints wrought, and ankles sprained.
On top of that, they would be extremely vulnerable to the predators inhabiting this world. On Earth, we were spear throwing, long distance running primates. On HeavyEarth, both running and throwing abilities would be severely handicapped. Catching food would be as probable as being food.
Many people would probably die in the first few months, if not weeks. Pregnancy would, in many cases, end up being deadly. The population would bottleneck.
Refuge would be found in salty water. The first generation would head towards the sea; floating would bring them relief from the weight of the world. Sweet relief from sore bones, joints and bulging blood vessels. Pregnant women, and new mothers would spend a lot of time in the water. Young children would grow up being very able swimmers. As on Earth, where the first human migrations followed the shoreline, so too would the transported humans. Net fishing would become a main source of food. The cultural practice of spending time in the water would be rewarded with longer life and more offspring.
Over time, adaptations would start arising that would be both advantageous to the gravity and also the sea. Stronger hearts, stronger veins, bigger lungs, stronger bones, webbed digits and upward pointing noses. Perhaps less hair and more blubber. Maybe even eventually an impressive dorsal fin...