1995 MGM wheels

does anyone know if it is possible to put newer 16" GM alloy wheels or steel wheels from say, a 1999 GM on the 1995 GM instead of the 15" steel wheels already on it... will there be any issues in clearence or whatnot... any reasons why i should not do this?

Your first issue will be the bolt pattern of the two wheels. If they're the same, then you worry about clearance. You can adjust the size of the 16" tires to be the same as the stock tires, just have to do some math. See
http://www.automotiveforums.com/vbulletin/showthread.php?t=311623

For discussion of tire size and sidewall height. Add double the sidewall height plus the size of the rim to get overall height.