I want to find a 95% confidence interval for difference in means of two sample groups. The mean of group 1 is 1583.467 and group 2 mean is 1017.933. S.D. is 757.0272 for group 1, and 512.5486 for group 2. Sample size for each group is 15. I came up with 483.431 confidence interval, estimating the difference at between 82.103 and 1048.965, which seems like quite a big range. Is this possible? Also, would the degrees of freedom be 14 or 28? According to my software d.g. is 28, but according to my text it would be 14. Thank you.