While the maximum space name length is 255 characters, this can be shortened for display purposes as required. For instance, in the place header this is based on the width of the rendered text, which has to fit into the banner. This is achieved dynamically in the web browser - if you use the Inspect Element tool on the title, you can see that the link has CSS properties "text-overflow: ellipsis" and "overflow: hidden", which determine this behavior.
Although there is not an out-of-the-box way to make this change, it might be possible with a customization. I would recommend you ask in the Jive Developers's space to see if any users/developers have made the theme customizations to allow them to change the stylesheet.
Hope this helps.