"which group could be more significant than others" is not a sound statistical question.
First off, and this is an important thing to learn, is that "significance" is a binary concept. One sets a threshold (typically alpha=0.05, as you've done), and then the coefficient either is or is not significant, depending on which side of the threshold the coefficient estimate lies. There is no such thing as more or less significant.
(The concept of effect size can measure the strength of the relationship between two variables, though.)
Next, it is not the group that is "significant" or not; it is the coefficient. So, if P<0.05 for that interaction term, then all you can really state is that an interaction of the strength you estimated (or greater) is unlikely to have occurred from random error, if the true interaction strengh were zero.
Finally, it doesn't seem sensible to me, if you only have two groups, to say "which one rejects the null more?". The model (I assume), is just testing whether they are different from each other.
Think more carefully and precisely about what question you are trying to answer. Perhaps, for example, you actually needed to build two models (one for each group against a baseline model), and estimate which group has a larger effect size. It's impossible to know, without a lot more context of your research question.
