15 year old maple tree (approx. 20 ft.) with at least 5 large main roots protruding above ground (and getting worse each year) on the north side of tree which is the higher(top) part of the yard (planted in middle of sloping front yard). Beautiful tree, but not sure what to do. If I grind down or cut out the protruding roots will it cause the tree to start leaning downward towards the bottom of the front yard? Should we cut it down now before it gets bigger?

The tree was not planted deep enough. I've run into this many times.

My recommendation would be to cut the roots that protrude above ground and hope for the best.

No, the tree will not start leaning because of it, but it may slowly die if too many of the roots are cut.

My guess is, though, that even if you cut several of the above ground roots, you will still have a dozen or more years of good life of the tree before it starts to suffer... OR the tree will live on and you'll never have a problem with it later.

That's my input based on my own experiences.