15' is more a medium or large-ish shrub than a tree. Many shrubs can be limbed up as small trees and will be a more appropriate size for a smaller, beach-city garden. A "small" tree is in the 25' range. Check the section of "patio trees" list in the Sunset Western Garden Book. Other ideas would be Pittosporum 'Marjorie Channon', Metrosideros 'Springfire', Eriobotrya deflexa, Magnolia x soulangiana 'Black Tulip' or similar.

Magnolia 'Teddy Bear' or Magnolia 'Little Gem' are a standard recommendation in Southern California, but they will eventually get much larger than 15' if allowed to (though it takes time) and can eventually develop quite a root system. They are "dwarf", yes, but keep in mind the non-dwarf version can get 60-80' feet tall. 30' is "dwarf" only by comparison.

'Marjorie Channon' is always described as 6'-8', but mine made it to 12' pretty quickly and without much care. At its very best near the ocean.

agree .... shape a shrub into tree form ......

the usual caveat is that trees really never stop growing ... so it would be very hard to find one.. that magically stops at 15 feet ...

you will either have to buy one that grows very slow.. so it a long time to 15 feet ... or you will have to be out there beating it back with a stick.. or saw ...

shrubs .. on the other hand .... seem to have limits to height .... but even those.. given decades ... can exceed the height ... but are more amiable to pruning them back ... rather than topping them ...

ken

You'd have to plant it on a mound for drainage, but check out Parkinsonia 'Desert Museum'. Ornamental all year, either bare, in leaf or in flower. Here it flowers for about three months.

Before looking at the table in the Sunset book - a good suggestion - look at the climate zoning section in the same publication, to see which particular Sunset Climate Zone you are in. Then you will be able to tell which shrubs/small trees* they think will grow in your climate, when looking at the table or reading the plant encyclopedia portion of the book.

The two critical cultural factors in this situation will be the close proximity of the sea and the clay-like soil texture.

*One height range designation system I think makes sense has large shrubs being those over 10 ft. high and small trees being those growing up to 35 ft. (With medium shrubs 6 to 10 ft. tall).