Difference between categories and sample


I've completed some research and categorised participants into 1 of 5 groups (independent variable), and then extracted a maximum data point for each participant (relating to driving speed) between 2 different scenarios - the data is NOT normally distributed and all participants completed both scenarios.

I would like to determine if all participants within the same group can be said to statistically have the same difference between the 2 scenarios, and whether there is a stronger effect for one group than another. As there were only 20 participants, the number of participants in each group ranges from 1 to 7.

Please may you help with the type of test that would be suitable. I will be completing the analysis on SPSS if it is suitable.

Thank you