You only have to remove the CMOS battery for a few seconds. 30 at most. There is barely any charge there that require waiting 15 minutes for it to reset.
Which also means that it could still be stored. A lot of newer mobo's have a jumper setting for the CMOS reset. Which need to be done instead of removing of hte battery.
So you should also check your mobo for small white writting by any jumpers to see if you ahve a CMOS reset jumper setting. If you do i would remove the battery. Put the jumper on the reset pins. Then put the jumper back to where it was and put the battery back. Then start the PC.