I cant find the document to back up my statements, but basically, could, but not advisable.
Why?
The processing power, drive space and memory are different in these servers. Basically, if your Publisher went down, the entire load is now on the 7815 server. Technically, you cant support a certain number devices on a 7815, where as on a 7825 you could support xyx (all depends on phones, gateways, etc)
For example, 7825 supports 2,000 devices
7815 supports 1,000 devices.
7825 falls over, down, reboots, whatever. Now the 7815 is overloaded, and then it crashes also.
It is best practice to use identical servers when using the Publisher/Subscriber model.
Cheers!
