Depends on which species, some are very tolerant of average clay soils without perfect drainage, while others need better drained soil or they tend to rot in winter. Echeveria imbricata, agavoides and secunda are several of the easiest to grow in the ground.

Summer sun is a bigger problem. They are unhappy in burning summer sun and do better with some shade.

RB

I would think zone 15 is a mild enough coastal climate that most of them are going to be perfectly happy in the ground.

I planted a bunch for a friend in Los Angeles and they do get rather ugly and die back a bit in the worst heat of summer (they need summer water) but then they perk up again in the fall and winter.

They thrive under shade cloth in the Bancroft Garden out in Walnut Creek, where it commonly gets into the 90's�F each summer. Ought to be fine with morning sun in San Jose, or dappled sun.