Is it possible that an incremental work may get selected by a top conference? I am a PhD student in computer science, working in theory. I was recently reading a research paper, which was submitted to a tier-3 conference last year.
It gave me some idea (which may not work), which is a kind of incremental, but yields a significant improvement of the run time.

The only problem I am facing right now is where I should submit this research paper. Although idea is not big as per me, my colleagues are saying it is significant and I do not realise as I have been working on this for three months. This is not related to my PhD project. I asked my supervisor and he said it seems okay to him.

Question: Is it possible that an incremental work on research paper may get selected for a top conference? I have hard time deciding to which conference I should submit. I have little experience as I have already published two research papers but that does not seem to help much.
It's possible, in the sense that there's a non-zero chance of acceptance. A couple of factors strongly contribute to this chance: How well can you explain the significance of the problem? How big is the novelty delta, for example, are there some entirely new concepts? How big is the runtime improvement? How rigorous is the evaluation?

In essence, you need to write a very strong paper, which is naturally easier for some contributions  than for others.