Ask Mr. Smarty Plants

This is what the US Forest Service says about Arbutus menziesii (Pacific madrone):

"Once established, Pacific madrone is windfirm, drought enduring and somewhat tolerant of wet, freezing conditions."  They also say that the root system is widespread and massive.

So, in answer to your question about whether the madrone is likely to fall on your house, I would so "no, not very likely." In answer to whether the roots are going to damage the foundation, I would say "possibly", but fifteen feet is a pretty good distance from your house for the roots to spread without damaging your foundation.

Given that there is concern about The Decline of the Pacific Madrone (Arbutus menziesii) and the fact that it is a beautiful tree, it would be a real shame to cut it down.  It might be possible to transplant it, but UBC Botanical Garden forum says that Pacific madrone is difficult to transplant since they are prone to disease and the process of transplanting injures roots so that pathogens are more likely to have an opportunity to invade.  Oregon State University Extension Service also points out the difficulty in transplanting the Pacific madrone.    You can see other posts concerning The Genus Arbutus on the UBC Botanical Garden forums.

In case you decide to try transplanting, here are a couple of informative articles on transplanting trees from the Agricultural Extension Service of the University of Tennessee and from North Dakota State University.

Also, you might contact the Linn County Office of Oregon State University for local assistance in your decisions about your madrone.