There could be two levels of timeout at play depending on whether task is being done via VC or not:
1. VC timeout, KB 1017253
2. VMware Tools timeout, defaults to 15 mins
In order to let the operation run longer than 15 mins, you will need to increase both timeouts. You can configure VMware Tools timeout inside the guest using tools.conf (refer KB 1007873 for tools.conf). Here is example setting for 20 mins (its measured in seconds):
[vmbackup]
timeout=1200
Ensure to set a smaller timeout value in tools.conf in guest than the VC timeout. Otherwise, VC could give up the operation before VMware Tools completes it.