Interesting, when I did a 100 meter Dronie this morning all of a sudden the feed became laggy (haven't checked the result in the app yet but it can't be good), might be related to the caching. Actually I switched caching to the SD card, maybe not a good idea as the built-in storage would be faster. That could explain why I was finding 4.1.15 to be a bit "laggy" compared to 4.1.13.
With 4.1.5 I lost the connection this morning over the water at 1.5km using the "range extender" which doesn't sound normal since I got 1.5km last week with 4.1.14over land without extenders.