A quick comparison between 2.3.13 v/s 2.3.15 v/s 2.3.15 with Hardware Encoding.
The time taken to complete conversion is measured in hours.
Source WTV video is:
Video codec: H.264
Audio codec : AAC LATM
Duration : 1hr 5min
Resolution: 1080p (1920 x 1080)
Processor: Intel Core i7 3540M (3.0Ghz)
Video card: HD Graphics 4000
OS: Windows 8.1 Professional 64bit
Max Resolution: 1080p (1920 x 1080)
Automatic Quality Detection: Enabled (default)
Quality: 0% (default)
Volume: 1 (default)
Cropping: Enabled (default)
As you can see there is about 25% increase in performance between 2.3.13 and 2.3.15 and about 1800% increase in performance between 2.3.13 and 2.3.15 with H/W encoding