I am also getting this slow experience as everyone described on my Note 4 with ExtSD Card. The remedy of using my internal SD card is not a solution I would like. I bought my Samsung 65GB USH-I Class 10 card. It claims to have up to 70MB/S Read and up to 20MB/s Write speed.
I did run a speed test and I received Read 14.87mB/s and Write 5.62MB/s.
Tap the take pics seemed to fix the problem of taking a picture at a slow speed.
Pictures being save to the gallery takes some time to complete, not an huge issue but when I go to the gallery to delete some images, this is where the problem occurs.
When I am previewing the image and I hit the delete button, nothing happens until a time frame of 3 seconds to 10 seconds. The work around for me is to delete the image on thumbnail mode.