Your card is according to Hercules' site a Geforce 2 based card . This is an AGP 2.0 spec card and you are therefore fine ........... the card works at 1.5 v .
Edit : Only some older TNT2 cards and the SIS 315 cards are AGP1.0 and don't support 1.5v . AGP cards newer than those such as yours have no problem . In fact yours may be able to run at the older voltage of 3.3 as well . This won't bother you with your 1.5v board . Most of the latest cards however now support 1.5v only as do most recent motherboards .