the original fuse is to protect the wiring which goes directly to headlamps. If you have installed relays in a way that the steering stalk only switches on the relays then the original 15A fuse is useless now. You need to install a new fuseholder in the circuit that you are using to power the headlamp bulbs.
Your amp draw at 100W is 7 amps per lamp- meaning a total of 14amps, you need to add 30% to this, so about a 20A fuse is minimum requirement for you. - not the original one though as its not even seeing 1 amp now.