Optimal time interval for scheduling of Transaction Log Backup
The main question to ask yourself is how much data can you afford to lose. That will determine how often you need to backup the log. But there is nothing wrong with running transaction log backups very often, even every minute. This accomplishes 2 things: 1. Provides you with the security that you won't lose data; 2. Improves performance - the less data you backup at any one time the lower your I/O overhead. 
I recently read a blog post stating that, from a performance point of view, log backups taken every minute greatly reduced I/O pressure. The downside of such frequently run backups is restoring them. As Bogdan rightly mentions in the comments, you should write a script to perform the restores. Depending on how far back in time you need to go you may need to restore a large number of transaction log backups. Doing that manually is very time consuming and prone to errors. There are probably third party tools that help with this as well.