Heartbeat Server is kind of a misnomer... it is a service in the 3300 that periodically "checks" its connection to various devices and services, when there is no response or a message is expected within a certain time frame, then it generates this message. My guess is the 1915 is the port it is using, 172.16.2.2:1915 would indicate it is trying to talk to a device at 172.16.2.2 on TCP (or UDP) port 1915.
It sounds like for some reason the link to a remove 3300 is being lost for a few moments, this could be the result of any number of network or hardware issues, from as simple as a bad cable to too many kids in the apartment building next door are streaming Crackle videos at 9PM and bogging out the area's bandwidth. Or this could be your IT department imaging mass numbers of computers after hours, totally bogging down the network momentarily. My point is that it's just an indication the 3300 sees something, but that in itself isn't much to go on, although you mention an IP Trunk Link is returned to service shortly after, look at that link (pings, traceroutes, etc) for anything unusual and check the logs in the remote equipment for indications of the issue.
That being said, sometimes the 3300 is a bit over zealous in it's logging, and you need to just ignore some stuff. If this does not seem to be service effecting, not getting worse, and not consistent, I would monitor it but unless something changes I probably wouldn't do anything at this point.
