I would just like to share a quick test I performed with 3 cameras to see each response time.
I used the google camera(stock marshmallow mra58r), HTC M9 camera (its here in the apps- first page), and Hydrogen OS camera (http://forum.xda-developers.com/oneplus-one/themes-apps/hydrogen-os-camera-oneplus-1-op2-t3241423
I really was curious how fast the google camera responds compared to any other camera. The time it takes to open app, and take a picture. I used a stopwatch for the tests and started the timer as soon as I hit the app for the camera and stopped the timer as soon as the pictured was taken (usually indicated by screen flash or whatever each app uses).
Test 1 was a three shot test (not burst shot-just took three successive shots). Each camera I tested 6 times(3 shots each time).
Google: avg time 4.88 sec
HTC: avg time 6.82 sec
Oxygen OS: avg time 5.49 sec
i)The google camera focuses the first time and afterwards doesn't really readjust focus unless significant movement is made in between shots. This would seem to be why the times are so quick for subsequent shots. However, this is why there is alway at least one blurry, terrible pic of the three.
ii)The HTC camera refocuses after each shot and all three pictures have good to great quality.
iii)The Oxygen OS camera seems to take the better road (perhaps just less bloaty app), it refocuses each time and somewhat faster. The picture quality is not noticeably different from the HTC pics, all three are good-great.
Test 2 was a single shot test. Each camera was tested 9 times (dunno why- just chose 9)
Google: avg time 3.22 sec
HTC: avg time 3.25 sec
Oxygen OS: 2.36 sec
i) Not all pictures turned out great here on the google camera. Only 6/9 were usable and good and not terribly blurry. Quite consistent (not enough tests to be statistically, but hey this was a quick thing I did) with Test 1 results, because ⅓ pics were bad.
ii) The HTC camera did comparably well in time, but the focusing was much better as all 9 pics were good.
iii)Oxygen OS camera was the fastest of the three and still managed to give great quality pics (just as good as all the good ones from the other two camera apps).
Final note: Basically it seems with our shutter speed its pretty hard to get under 2 seconds to get that first shot and have it be good. I’ve noticed that if I'm doing anything with lots of motion, like if I’m out climbing then someone takes a picture of me with my phone; most of the shots are unusuable. At least the oxygen app is the snappiest and I will now start to use that as my default camera app.
P.S. will try other cameras in the future too. I didn't post pics because I thought for the quickness of these tests it would be a pain to upload all of them.