Ok, went through the nvm settings for the c405 I thought would apply, that also weren't invalid, on the 6515.
The one I thought would do it was changjng the line type for Ch0 from PBX (value 1) to PSTN (value 0), nvm 823-036, but still wakes up every 30 minutes with the VOIP phone line plugged in. The other line types for the other channels are already PSTN.
I also changed the values of "fax card hook detection threshold voltage" values up and down 2 for 826-004, 005 and 006 (6, 10 and 20 respectively) just in case the voip line voltage was changing during those episodes, triggering the wake up. I didn't want to go too far from default.
I don't fax all that often but would like to have this work properly.
Picked up a WC6515 a few weeks ago. Works great other than every 30 minutes, with the phone line connected, the 6515 wakes up. I installed the latest firmware (released this week) and still does it though this version didn't mention a fix for this. My old Canon f170 didn't have this issue. I'm thinking there is something from the voip modem that tricks the machine into thinking there's a call coming in. It also wakes up when an extention is picked up.
It there an NVM setting for the fax to make it less sensitive to line voltage changes? I'm a tech for XBS and couldn't find an NVM list in the manual or in a GSN library for this product.