Fuse for reverse lights for 1995 Golf GTi

Hello. I am just wondering if anyone knows what the correct fuse size
is for the backup lights on a 1995 Golf GTi? The fuse that was in there
was a 15w; however, every time I try to replace it, it blows as soon as
I turn the key to the 'On' position. The fuse panel cover neglects to
mention what size the fuses should be. If it is the right fuse size,
then I know I will have to check for a short in the wiring system.

Thank you for your reply.