There are good reasons to choose an unamanged language, but this part strikes me as odd.

"my last project was Java. C++ would have allowed us to port more easily to other platforms"

I'm not saying that you must wrong for your particular situation, but as soon as you've compile Java, you've essentially ported it to a massive number of platforms. https://en.wikipedia.org/wiki/List_of_Java_virtual_machines

If anything a dependency on OpenGL would limit your choices.