Is It Reasonable to Say Invisalign Are Worn All Day, Except for Eating and Brushing?

The research and design has shown the aligners to work as directed, 20-22 hours per day.  Any deviation from protocol may give unpredictable results.  Can it work with 15 hours per day?  Maybe.  Will it be stable and last?  Don't know.

But with an investment like that for Invisalign, it would make sense to get the best ROI possible.

Yes, it is correct to say that Invisalign must be worn nearly all the time except for when eating and then brushing and flossing your teeth.  We recommend at least 22 hours per day.  If the aligners are only worn 15 hours per day, as you asked, then there will definitely be problems.  There will not be enough active time in the day for the aligners to work.  There will be problems with the teeth tracking (fitting in the aligners), and the teeth will not get as straight as planned.  There could actually be a point when the aligners do not even fit on the teeth.  

Not only is it reasonable it is critical. You will absolutely compromise your result by getting any less wear. It is a lot of money to to throw away. If your life style or personality doesnt allow you to commit to 20-22 hours everyday of wear DON'T DO INVISALIGN.