How to remove encryption in Marshmallow without root? Encryption is making transferring of files from phone to PC really slow besides I want to open my phone without any prompt and jump directly to my work.

As far as what I've tried is to go to settings but nothing occurred on tapping encryption.
As my phone is in warranty and and also not popular (Eluga Tapp) root not seems to be a viable option.
A factory reset will remove the encryption. After doing this you might want to install a custom recovery, just in case. There are many tutorials to do this in the internet.