Sounds awful. 15 fps 4k is not very useful. For a quarter of the price you can get a stunning ultra thin phone that shoots 30 fps video very well. I am talking about the OnePlus One. Or for a third of the price of the Panasonic you can get the Oppo Find 7a which shoots longer 4k videos.
My RX100 ii was put up for sale immediately when I realised how much better the Oppo is. The difference in color and detail is unbelievable, the Sony is miles behind. Sony and the rest are holding back the technology, so people into certain videography like me have jumped ship. Phones are the way to go at the moment for ultra cheap ultra HD video, which is actually pretty good. There is probably no need for most people to buy this massive brick made by Panasonic.