Standard Pacific is a reputable builder. They continue to build new homes in nearby Dublin and from what I've experienced with buyers who have purchased SP homes in the last 15 years is that they are very happy with the quality of workmanship. I would compare SP in line with Shapell which is another major builder in San Ramon. How well a home is maintained is what you should focus on however. An experienced inspector can go over any deferred maintenance and major home repairs needed. Hope this is helpful.
The bigger issue is not the quality of build - in reality, any problems would more than likely have been discovered by now. The real issue is how well any given home has been maintained over the past 15 years. A competent set of building inspectors can find any issues.