What to do with a (underwater) $1.45M property with a 2.78% mortgage...?

[Trent Dyrsmid]

2.5 years ago, we sold a house we'd owned for two years for $900K (paid $480K) and we used the proceeds to buy our current house in the very best neighborhood in Boise for $1.45M and then we spent another $150K (in cash) on improvements. 

Our mortgage is at 2.78% for 30 years and our mortgage payment (inc taxes and insurance) is $6K/mo. Our monthly income is just over $20K/mo before taxes. 

Last summer, we were away for a few months and we made $25K from AirBnB on this house. This year, we won't be away for the entire summer, so I estimate we'll earn about $12-14K from AirBnB (house rents for about $400/night).

In hindsight, we bought too expensive of a home, and the problem I'm trying to solve is that I HATE having a $6K mortgage payment....but we LOVE the house and the neighborhood.

Options I see:

1. We could sell the house..but it is not worth what we paid, so we'd take a significant loss, plus we'd be walking away from a 2.78% mortgage
2. We could AirBnB it more....but then we have to incur the cost/inconvenience of being out of the house more often
3. We could build an ADU over the detached garage..but we'd have to refi the mortgage and we'd lose the 2.78% rate

When it comes to lowering our house-related expenses, what am I not seeing? I would love to hear your suggestions.

Thank you!