EPSG/POSC code 26915 - 2 related questions on using this projection in ArcGIS

Hello,

I am obtaining data from a colleague in Africa who has been collecting data using EPSG code 26915 (or POSC?), with datum NAD83. I am not familiar with this projection and it appears that it is actually a default code (for Minnesota, UTM N15).

First question - what projection do I use for this data in ArcGIS? EPSG, POSC codes do not seem to be used in Arc and do not come up in Help topics. How do I project it in Arc? (I have an excel table of southings and eastings.)

Second question - if my colleague has been collecting data supposedly in southern Kenya (around the division between UTM grid 36 and 37 and just south of the equator), but using the EPSG code 26915, is the data still usable? Can we convert it to the proper projection? Or since its been collected in an inappropriate projection, will we ever be able to get the 'true' coordinates?

thanks for your time,
Andrew