Nicholas --
Since Confederate companies were normally recruited in specific communities, it's important to know where your family lived in 1860. Your college library may have a subscription to Ancestry or something similar which will allow you to search the census for specific counties in Mississippi. Once you get the hang of it, it's a useful tool.
The Mississippi SCV has sources which will help identify companies raised in each county. Pension applications are another useful source of data. If you have questions, post them here and one of the experts on this board will offer to help.
http://www.mississippiscv.org/research.html
The NPS index suggests there were at least six Henderson men in Co. "I", 15th Mississippi Regiment. If you have any names, order copies of military service files from the message board link below.