Setting frameRate(30) doesn't guarantee that you will get 30 frames/second, it just gives the program a target to aim for. If your computer can't run the program at 30fps, it will run it as fast as it's able to. You can use println(frameRate) to check how fast the program is actually running. 

On the other hand, instead of running your program for a given duration, you can use frameCount to stop your program after 7020 frames has been saved.
Note that saveFrame() can actually be a cause of the low framerate... You can try and save your frames to a fast USB device or a virtual Ram disk.

If it doesn't have to be real time, there are a couple of ways to approach this: 

You can try my suggestions above for fast saving (virtual disk is the cheapest solution).
There are also lot of threads about this issue of capturing sound and image simultaneously (not sure if there is a definite answer).