This is where you ask yourself "would I like if someone releases a product with the exact same name as my company's and moved us to the second page of Google?".
Even if that was somehow relevant (it doesn't really matter what you called it internally if you didn't use the name publicly), the existing Q.js is older!
You may have started two years ago but you only open sourced it for the community two hours ago.
that is a bit childish. the time you began development is not relevant, and seeing as q.js is already popular, it is safe to say it will stay that way.
changing the name is great advice. consider it.