Add time (duration) to timestamp

[Jarmo Hurri <jarmo.hurri@iki.fi>]

Greetings.

Is there a way to add time to a timestamp, say, in a table?

For example, say I have a series of events, each lasting 15 minutes,
starting at a specified time on a specific day. I want to create a table
of them as follows:

| time                       | event |
|----------------------------+-------|
| <2015-12-07 Mon 12:00>     | A     |
| add 15 minutes to above    | B     |
| again, add 15 min to above | C     |

Is there a way to automate the generation of the timestamps of events B
and C?

Jarmo