Can I still help my spouse with his papers if I did my time 15 years ago?

Generally a U.S. citizen's criminal conviction record from many years ago will have no impact upon eligibility to sponsor a spouse for immigration benefits. Of course, there are many details that determine eligibility for a marriage-based adjustment of status case. It would be wise for you and your spouse to consult with an immigration attorney who, after learning all of the relevant information, could advise about eligibilities, options and strategies to attain your goals, and who then could offer legal representation in the often complex application process.