You haven't included enough information. Yes, you're waiting on latches (Mutexes in Unix) but before you look at Informix look at the operating system.
Check release documentation and find out what the recommend kernel values are for your release. Check these against actual values - and remember, the release documents assume this is a dedicated Informix server. If something else runs on this server you need to factor.
Is this a new problem or ongoing? Fess up - what changed?
Check onstat -s and see who's hold in the latches. If no one is and everyone's still waiting, you're short at the operating system level.
How many users, how many CPU's (defined vs. actual) - and once again, are you the only player on this box?