There really isn't enough information to provide a sufficient response.
1- When you say asymmetrical, should the understanding be that all the traffic leaving the site is using the primary link, and that it is only the traffic going to the site is where you are seeing utilization on the secondary link? (In other words in only one direction?)
2- What routing protocol(s) are in use?
3- Is this a private network, or do you mean from your office to and from the Internet.
4- If a private network, do you direct peer with your remotes or are you relying on a provider in the middle for connectivity?
Answers to these questions would be a good start and a diagram would also be helpful.
Thanks