Nope it does render faster
I just tested it.
I rendered the cube in default, it took 5.62 seconds.
I then rendered the cube in preview, it took 1.06 seconds.
I then rendered the cube in default again, it took 1.10 seconds.
Here’s a second shot at it (hope you can read the numbers). Default start up with no changes:
First time render using default 800 x 600, Asp X = 100, Asp Y = 100, 100%, time take = 5:25 seconds:
Second time render using preview, 640 x 512, Asp X = 1, Asp Y = 1, 50%, time taken = 1:05 seconds:
Third time render using default, 800 x 600, Asp X = 100, Asp Y = 100, 100%, time taken = 1:12 seconds: