[pron]

I would first spend a good amount of time figuring out if you can't just keep it in Java, because it's not just the rewrite in C++ that's expensive, but a low-level language would make maintenance and evolution costlier forever.

If memory footprint is the issue, I would recommend watching this: https://youtu.be/mLNFVNXbw7I. A lot of people misunderstand memory consumption, and even in Java there are many options to try. There could definitely still be situations where a low-level language is the only choice, but it's not a decision to be taken lightly.