It might be an "old" topic, however, it appears similar to my situation now. And I am also considering to look for another PhD position, although I am a bit "mature" PhD student already...however, I am not satisfied with my progress and am wondering will I really finish this by knowing anything in the end. 2,5 years might work if you have already been working on the similar topic and in the same lab. But when you change the country, don't know anything and are new to the topic, it can seem impossible. You would need to be really lucky or to have a PI who knows what he is doing. Are some decisions made or is there any update on you situation? Good luck.