There are 2 different Bajaj 150s, the Boxer and the Pulsar.
The Pulsar is more of a sportbike, the Boxer is a commuter that's built to take rough handling and comes with a decent rack, big comfortable saddle and relaxed ergonomic.
I can't speak to altitude use, but the Boxers are used around here a lot as 'habal habals', or bike taxis, carrying 3 to 6 people and sometimes more, on the road or on tracks up in the mountains.
Likely you will need to change sprockets for more torque in the hills, although the gearing is already quite low so you may be ok.
Try to Google them, I've seen Indian reviews and tests before. Google for some tests,
is one example.
The Pulsar with likely do the job as well, but it depends on what ergonomics you like and will more likely want to change the gearing.
Here the Pulsar comes in 135 and 220cc variants. They are very heavy for what they are, but seem to be robustly constructed.
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