Dear Sir:
Thank you for the sample.
The conversion process you applied to produce this file make a linear DNG, that is the file is demosaicked. That means 4x more data after unpacking. Of course the processing is times slower.
On top of that, the file contains lossy 8-bit data, here is the relevant portion of metadata
[EXIF] 0x0102 BitsPerSample: 8 8 8
[EXIF] 0x0103 Compression: Lossy JPEG
[EXIF] 0x0106 PhotometricInterpretation: Linear Raw
[EXIF] 0x0115 SamplesPerPixel: 3
If you are forced to use such a format, please try setting
Preferences -> "GPU Processing" -> "Process RAW data on GPU" to "All raw files" - that will speed things up a lot if your video card / GPU is one of the modern models.
Dear Sir: