You can stake it and that will most likely extend it's life, but it's a reasonable assumption that it's on its way out. Wind and roots and a top-heavy tree.

If your mesquite is fifteen years old and has never been watered, then you will not be able to find a "more natural to the desert" tree anywhere. The solution, I think, lies in an observation that the tree (and the one behind it) have not been pruned well.

As for it falling on the wall, check your homeowner's insurance policy. At my house we have twin fifty year old 65 - 70 foot palms and, with the deductible, it will be cheaper to let them fall on our neighbor's house (and car) than it would be to have them removed and the stumps ground down. Our insurance agent backs that up. Go figure.

Too big to stake it. Cant just tie a rope to it and straighten it, plus would look terrible. Remove it and if you want another Mesquite, take care of it properly. The reasons why you often see Mesquites do this (especially Chilean Mesquites) are several:

1) they do not have their own irrigation valve separated from the shrublines which require more frequent and shallow watering compared to trees - thus resulting in shallow roots

2) they are overstaked or the stakes are not removed so as to allow the trunk to develop a strong tissue to withstand windy conditions

3) they are not pruned properly by not thinning out the canopy so the wind can blow through them (they are fast growing and can get top heavy)

Thanks for the pic and for starting the discussion. If it was my tree, I'd have it removed and I'd replace it with something else. As you know, and others mentioned, they can get very top heavy and prone to blow over, especially if they are watered a lot or develop a big fluffy head. You were smart to stop watering it when it was established (I have a humongous one that came with this house and I eased it off of drip irrigation and haven't watered it in six years now). Maybe even try for something a bit more compact, like a Texas ebony, or even a Texas mountain laurel (toxic seeds)? Either way, *I* would remove it and replace it.

Let us know what you do and how it works out! Happy gardening!