I'm wondering the same thing, I've got a snom 715 that we're trying out. I haven't been able to provision the snom 715 and thought I would mention that gmcda isn't the only one with this issue.
Is the snom 715 supported? The snom 700 series is listed in the preferred phones list: http://www.3cx.com/sip-phones/, but it only lists 710, 720, and 760. Snom says "3CX Phone System is fully compatible with the snom 320, 360, 370, 7xx, and 8xx desktop phone series" http://www.snom.com/it/partners/trova-il-rivenditore-piu-vicino/interoperability-partners/advanced-interoperability-partners/3cx/. However, from the main page of their website http://www.snom.com/en/nc/ there is a link to "NEW: Snom 715". Maybe the page about being compatible with the 7xx phones was written before the 715 was released? I looked for a date that the snom 715 was released on snom.com and on the wiki (http://wiki.snom.com/Main_Page) but couldn't find anything.
I'm in the process of evaluating both a snom 715 and a snom 720. From the 3CX console, the 720 appears in the list of phones, but the 715 does not.
If the 715 isn't supported but is easy to provision by adapting the 710 template that might be an ok solution, but if not it would be good to know and we'll buy different phones (maybe the 720).
Any suggestions from someone who has attempted to set up a snom 715 with 3CX would be a great help!