Are you saying that the size of disk space taken by some projects is very large or that TestComplete consumes a lot of memory when opening the project? (or both?)
If you have a lot of log files that you don't need, remove them from the project(s). If you don't need visualizer images, turn that off in your projects.
It might be that a particular project is consuming lots of memory. If you want to do some investigation, make a backup of your project suite and then..
...try 'removing' all but one of your projects from your project suite and then close and reopen the project suite to see how that affects the amount of memory used. (Use 'remove' not 'delete'.) Add back the projects into the project suite as 'existing items' one by one to see how memory usage is affected.
Is there one project causing the problem?