I'm facing a dilemma now and I would like to know what you think about this situation. For several years, I have been a self-funded part-time postgraduate student working on a dissertation in field X at a high-ranking university while I was doing all kinds of jobs to sustain myself. After so many years, however, I got an offer from another university to do a fully funded Phd with them. Financially, this new PhD project will give me much more stability and less worries, so I accepted it, even if it's another subject in another field. Having completed huge amounts of fieldwork and several chapters for my previous PhD project, I feel bad to abandon my previous project. I invested so much time, energy and money in it... I cannot believe I did all this for nothing. To complete the previous PhD project, however, will still take me quite some time and I have to pay the high tuition fees again. I'm afraid it will be difficult to combine this with my new Phd project. However, I really want to finish what I started. So, my question is if you think it would worth finishing the old Phd?

I think you need to ask yourself why you are doing a PhD? Is it to get a job that requires a PhD? In which case option B as you will get one quicker. Your previous work isn't lost, after PhD you can always go back and finish the other project but without the pressure of completing it as a PhD, you could write it up as a book or journal articles with no pressure to pass a viva! Of course getting published is another difficult journey.