Sisu R500 Cummins and Cat C15 sound mod

Note from the Author:

Hi, i had few requests for this, so i decided to update the sounds for the Sisu R500 by RJL.

This mod adds the Cummins N14 and Cat C15 engines sounds, and two 18 speeds gear boxes.

Truck can be found here :

SISU R500, C500 and C600 V1.1.5 [1.22.x]