I am looking at the latest Camera Remote SDK 1.21, released on 2013 Dec 3 (http://developer.sony.com/downloads/all/sony-camera-remote-api-beta-sdk/). But there are currently no support on taking "interval still" (a.k.a. timelapse) photos on HDR-AS15/30.
I think the "interval still" shoot mode is one of the core feature on Action Cam. The current set of API allow developer to switch shoot mode to "interval still", but we are not able to start recording timelapse video.
I don't see any good reason why "startIntervalStillRec" is marked as private for now.
I know opening up every single API may compete with the "Camera App" system built into the NEX-5T/R, which will be undesirable in Sony current perspective. But maybe Sony can make a developer registration system and provide keys to access limited APIs without forcing us to break into the Android APK file.