Chief -- you won't believe it but to change the chassis battery in the 2015 you will have to go through the top of the dash on the passenger side. You need to remove the computer desk and there is a cutout area you have to remove. I included the link to the Vegas/Axis owners manual I compiled. There is a description and pictures showing how to remove the chassis battery. The link to the manual is:
https://1drv.ms/w/s!AiYx6DLSeiiP6UNyy_VYGDO0BW6L