title: Add 15 minutes to current timestamp using timedelta
body: <p>The title says it all. I am writing a script to make scheduled GET requests to an API. I want to print when the next API call will be made, which would be 15 minutes from the previous call. </p>
  
  <p>I'm very close, but have been running into the following error: <code>TypeError: a float is required</code></p>
  
  <p><strong>Here's my code:</strong></p>
  
  <pre><code>import time, datetime
  from datetime import datetime, timedelta
  
  while True:
      ## create a timestamp for the present moment:
      currentTime = datetime.datetime.fromtimestamp(time.time()).strftime("%Y-%m-%d %H:%M:%S")
      print "GET request @ " + str(currentTime)
  
      ## create a timestamp for 15 minutes into the future:
      nextTime = datetime.datetime.now() + datetime.timedelta(minutes = 15)
      print "Next request @ " + str(datetime.datetime.fromtimestamp(nextTime).strftime("%Y-%m-%d %H:%M:%S")
      print "############################ DONE #############################"
      time.sleep(900) ## call the api every 15 minutes   
  </code></pre>
  
  <p>I can get things to work (sort of) when changing the following line:</p>
  
  <pre><code>print "Next request @ " + str(nextTime)
  </code></pre>
  
  <p>However, this prints a timestamp with six decimal places for milliseconds. I want to keep things in the <code>%Y-%m-%d %H:%M:%S</code> format.</p>