CaraVR is designed to perform very intensive calculations, so it will always take a while to process, however there are a few ways to gain some performance improvements.
1) Read and write files to an SSD, rather than a mechanical or network drive.
2) Reading and writing .DPX files rather than .mov or other video formats.
3) Increase the amount of VRAM Nuke can use. This can be done in Edit>Preferences...>Performance/Hardware, then adjust the GPU texture cache size to match the amount of VRAM in your system.
4) For Late 2013 Mac Pro's you can also enable multi-GPU support, from the same preferences. Information about this can be found here, at the bottom on the page:
5) You can also use the GPUs to accelerate the Viewer and inputs when possible. This can be found in Edit>Preferences...>Panels/Viewer, then turn on the two options.
6) Downrez your preview in the viewport, the option can be found in the top right of the Viewer panel, as shown below. The lower the ratio, then the lower the quality, but the faster it will render in the Viewer*.
7) Precomping after the C_Sticher should help later nodes perform faster, but only do this when you are happy with the stitch.
8) Upgrading to the latest version of Nuke and CaraVR should bring some speed and stability improvements.
9) Run multiple instances of Nuke when you are rendering. So each instance renders a different frame range into an image sequence. This sequence can then be read and exported into whatever final format you need. This should use more of your CPU power, and give you a quicker render.
Depending on your system and your shot, the performance gains from these suggestions will vary a lot. Below are some results from testing how VRAM and drive type affect how long CaraVR takes to playback a 100 frame, DPX, 8 camera solve.
As you can see, on this machine, increasing the amount of VRAM gave slight improvements, whereas switching to an SSD gave significant improvements.
The next graph compares the amount of time it takes to solve the same shot, with different file formats for a single frame.
As you can see, both the Prores and H264 video formats are slower then the image sequences, and DPX is the fastest of the image sequences.
All this data was gathered on one machine, and may not reflect performance improvements that you experience.
*There are some known issues with using proxy mode for CaraVR, so please use it with caution. If you do find any issues with it, please report them to email@example.com.