Huh? I'm not quite sure what you're asking.
Those edits should work fine. That would create:
vpn.tm.local -> 192.168.15.3
192.168.15.3 -> vpn.tm.local
You should always increase your serial number in the SOA record for every change you make though. It doesn't really make a difference if you have 1 server, but if you have more than 1 that's how they know they need to do a zone transfer. Typically the serial number is in the format of the date+revision number:
yyyymmddXX for today would be 2010010801, where the last two digits are the number of changes you made that day. 01 for the first change, 02 for the second....etc.