I am bit confused on what statistical test to use on SPSS. I am investigating whether a low calorie diet with prescribed exercise is more effective than a low calorie diet without prescribed exercise for weight loss.

There was 2 groups with 15 participants in each group. The primary outcome measure is BMI. Assessments were performed at baseline, 6 weeks (halfway through intervention), 12 weeks (end of intervention) and 24 weeks (follow up).

Any suggestions would be helpful thank you.