While the 2015 Highlander awaits its official introduction, Toyota has gone ahead and made an electronic (and searchable!) version of the owner’s manual for the 2015 model year available online at toyota.com/owners.
To access it, visit the link above, click on “Resources > Manuals & Warranty” and then click the red button to “Choose a Vehicle.” From there, select “Highlander” in the model pulldown and “2015” in the year pulldown.
Note that if you’ve already been using the Toyota Owners portal, it might default to your current vehicle when you load it up. In that case, you’ll need to click on the top left tab (mine says “2014 Highlander”) and then choose a different vehicle.
I haven’t read through it closely but, given the similarity of the 2015 model to the inaugural 2014 model, I doubt the manual has changed much from last year. A quick spot check revealed that the engine break-in tips are identical, and on the exact same page.