I am sorry for the delayed response. Create a new project in AfterEffects CC 2017 version & import the AfterEffects CS6 project file into the new project & try to export.
Please let us know the status.
**Edited by Vidya Sagar
There can be a number of reasons why something would render differently speed-wise between the two versions. Some things render faster in the new version and some things will render faster in older versions. A lot of it depends on whether or not your composition and computer system can benefit from multiprocessing. Some of it will depend on differences between AE's render queue and the Adobe Media Encoder.
One thing to try, work on your project in CC 2017.1 and then save it as version 13 and open it in CC 2014. Try rendering it there and see how it behaves. (You can download all versions of AE from CS6 through the most current and install them alongside each other through your CC subscription. Details here.)
Another thing to try, render out of AE into something like a Cineform codec and then use AME to encode your deliverable.
See where there are any speed differences.
As someone who works on deadlines, you will probably appreciate how much easier it is to send an AE comp directly to the Adobe Media Encoder in the newer versions. You can finish your work, send it to AME, and then move on to the next project and keep working while it encodes in the background. Big time-saver compared to waiting for AE to render!
There are several things on that list that are no longer supported in After Effects. H.264, Windows Media, FLV, and others.
More info here: