Messages should be grouped by tranches of more than 1 minute in conversations

When sending messages, the message time line will be shown for every first message of a given minute.

For exemple:

--- THU 10:00PM ---  
received1  
              sent1  
              sent2  
--- THU 10:01PM ---  
received2  
              sent3
--- THU 10:02PM ---  
              sent4
received3

This makes conversations unnecessarily spaced out and heavy. Instead of every minute, messages could be grouped by tranches of 15 minutes (exemple). However, it would be important for the user to have a way to know at what time a was sent, thus we could have a single tap on a message show the time at which it was sent (or other user-friendly way to show it on demand).