2015 Toyota Highlander: enough for a 17' Hard-sided camper?

If you take two minutes and download the Toyota trailering guide you will get exact towing capacities for all their vehicles (which varies by engine).

I would take 2/3 of the maximum as the weight I would want to actually tow with a SUV. This leaves a buffer in terms of performance when towing which includes your ability to accelerate and merge with traffic, the ability to pass a tractor with double trailers going 10 MPH up a grade, and the ability to stop the SUV and the trailer in time in an emergency.