It's strange that nobody has explicitly mentioned it, but I think you should start with clearly understanding your own goals. Why do you study for PhD?
Is it just get a PhD badge and switch to industry? Is it get a PhD and move to another "average" group? Get a PhD and then move to a top-level group? Etc
In some of these goals (at least in the first, maybe in the second too), it does not really matter what is the quality of your research, what matters is a PhD badge. In this case, the next question to ask is very simple: what about PhD students in your group some 3-6 years older that you? Did they get their PhD? Based on what work? What do they do now? You may find that they did get a PhD with a work similar to what you are doing. In this case you have pretty good chances to get a PhD too, and that's all that matter.
In fact, sadly, in many parts of the world there are tons of really weak PhD awarded. In many places the majority of all PhDs are no novelty at all and are "hopeless" as research. Obviously, a good student should do some due diligence and avoid such places, but if you got as deep as 18 months into this program, it may be better to complete it and move on. Even such a PhD may be useful depending on your goals.
For example, I think that in industry they will not care what your research was, and moreover they will be pretty aware that there are many places like yours, and that it's not you to blame. Similarly, many "average" research groups in your city or uni may also be well aware of this, and will not judge your PhD research, but will judge your skills. So after you get a PhD, you may be able to switch to a better group and start a real research.
At the same time, if you plan to apply for some relatively top-level research group, then they will judge you by your work. In this case you need to get better research now. You may try discussing it with your advisor, although personally I don't think it will get any good results, or you need to switch advisor or PhD program in general.
So, think of your goals, study the carrer of PhD students from your group who are 3-6 years older than you, and after that decide.