It's going to take close to a decade for them to waste 15,000 assuming your managing it with temp settings and no open windows in the Winter, etc.I'm guessing since you are anticipating these upgrades that you are paying a price that justifies them. 

Do not allow them to manipulate you and reschedule.

They’re a little more spendy, but they’ll operate at 100% efficiency down to 5 degrees ambient outdoor temp.

Hey @Isabella Donadio, here's my experience from being a landlord for the past 14 years1) I primarily focus on Tempe and the areas around Arizona State University (see #2 for reasoning). 2) The properties rent almost immediately and are never vacant for more than a week.

You really can’t manipulate health and army factor to move. 

You might refer to what happens when others come up with creative schemes to manipulate the market (other people or institutions buying):https://www.marketwatch.com/story/two-traders-arrested-over-alleged-manipulation-of-more-than-2000-stocks-2016-12-12

Slim Mitsubishi air unit which is a lot less than central air and can solve their problem for the few summer months that the temps will be uncomfortable.

I already have land w infrastructure going in for another venture and thinking about the tiny house rental on it for a temp light cash making but if you search VRBO/AirbNb for comps you’ll see they aren’t heavy cash makers, mostly due to the smaller season.  

Builders use various appraisal & other manipulation means to inflate values.

These are wifi so you can monitor temp setting, actual temp and humidity.