Here's the datasheet if you can get it to load. Their website is agonizingly slow, at least for me (probably faster if you access it from china - I've seen that before) - it never loaded for me. I suspect it's written in chinese, though...
http://stcmcu.com/datasheet/stc/STC-AD-PDF/STC15.pdf
Update: It's in english, if you wait long enough. I've seen worse datasheets. Looks like it's a modernized replacement for a 8051-like micro. ISP programming is overUART (!) and they have GUI tools to do the flashing. Huh.