I tried it, but still take a lot of time for five seconds.
I think that there is the different cause.

A rendering domain is small in the latest build.
Does it contribute to take rendering time more?

Before build

Are you using auto tile size addon?

No, I do not use it.
However, I validated it, but the result was the same.

Though I open the same blend file, the default size of the tile is different.
I make tile size the same and tried it, but after all the latest build is slower.
(I tried it again in Hash:69470e3.)

I found something.

Error Message

File "F:\Blender_Git\build_windows_Full_x64_vc12_Release\bin\Release\2.78\scripts\addons\render_auto_tile_size.py", line 149, in engine_is_gpu
  return engine == 'CYCLES' and device == 'GPU' and userpref.system.compute_device_type != 'NONE'

AttributeError: 'UserPreferencesSystem' object has no attribute 'compute_device_type'
Traceback (most recent call last):

File "F:\Blender_Git\build_windows_Full_x64_vc12_Release\bin\Release\2.78\scripts\addons\render_auto_tile_size.py", line 177, in on_scene_update
  threads = get_threads(context, device)
File "F:\Blender_Git\build_windows_Full_x64_vc12_Release\bin\Release\2.78\scripts\addons\render_auto_tile_size.py", line 208, in get_threads
  if engine_is_gpu(engine, device, userpref):
File "F:\Blender_Git\build_windows_Full_x64_vc12_Release\bin\Release\2.78\scripts\addons\render_auto_tile_size.py", line 149, in engine_is_gpu

@Sergey Sharybin (sergey)
No, I did not use it.
I ran it in factory settings and chose GPU device and tried it after I set 0.05 for light sampling.
Because you asked me about that addon, I validated it later.

Did you check that tile size is the same across rBcf8f6d1 (the one which was fast for you) and the current latest builds?

@Sergey Sharybin (sergey), @Brecht Van Lommel (brecht)
I tested it in the latest build. (Hash: e17b92f)
I excluded that addon, and rendering was completed in the fastest time when I set most suitable tile size. (50sec)
Thank you for advice.

I'm sorry.
I thought that I reported that it became same as the past to you.

@Sergey Sharybin (sergey) Sharybin (sergey), @Brecht Van Lommel (brecht) Van Lommel (brecht)
I tested it in the latest build. (Hash: e17b92f)
I excluded that addon, and rendering was completed in the fastest time when I set most suitable tile size. (50sec)
Thank you for advice.

I confirmed it in Hash: 411836d.
Thank you.

Processing time becomes 5% long.