Comments

Steve Grisetti wrote on 9/24/2015, 7:54 PM
BluRays have a certain level of compression, which is what the 15 probably represents. I'd expect that regardless it should look as good as the original at 25 Mbps.
Former user wrote on 9/24/2015, 9:29 PM
Those numbers determine the Quality of the encoding. In most cases, 15 is a good compromise between quality and time. I always put it max though so I am sure I am getting the max quality.

It basically controls how much time is spent doing the math.
musicvid10 wrote on 9/24/2015, 10:03 PM
Those numbers are neither about compression (except indirectly), nor are they much about quality.
They are "usually" about how much effort goes into interframe motion estimation, which usually cannot be seen, but directly affects encoding time. You should be able to save a preset with a higher starting value if you wish, but at 25Mbps it isn't going to make a lot of difference, perhaps moreso if your source is animation.