The percentage CPU being used is irrelevant, for most cases. Your app will be killed if it takes too long to start up, which is time spent loading the storyboard, but it's time that matters, not CPU load as such. Unless you're pegging at 100%, don't worry about it.
Test on the device - if it launches, you're fine.
Building views in code is not necessarily faster or lighter on the CPU than using storyboards.