Wi-Fi is slow; non-infrastructure Wi-Fi doubly so. Most devices don't support IBSS (ad-hoc) networking in 802.11n or 802.11ac mode because being a base station requires multiple antennas in those modes. As a result, if you're tethering over Wi-Fi, you're probably limited to 802.11g speeds (54 Mbps over short distances, slower over longer distances).
With that said, if your numbers are accurate, it should not be that slow. Even over ad-hoc Wi-Fi, in 6 seconds, a camera should be able to transfer a 30-50 MB image. If it takes that long to transfer a 5 MB image, that's only about 833 kbps, which is appallingly slow even by 802.11b standards.
Technically, the minimum speed for 802.11a/b/g/n is 1 Mbps (typically at ~150 feet or so), so if you're getting less than that, you're either getting horrendous packet loss at the very fringes of the radio's range or:
- The software is badly written
- The camera doesn't start transmitting image data until after it finishes writing the photo to the flash card
- Your cell phone is slow
- Some combination of the above
You might try changing Wi-Fi channels if your camera allows you to do so, just in case it is an interference problem. But otherwise, such poor performance is likely indicative of a design flaw in Samsung's software/firmware, and there's not much you can do about it except complain until they fix it.