If your bike is only 15# it is a $1,000+ bike. If it was mine I would
pack it in a hard case for air shipping and put it inside the trailer or
tow vehicle.
Bikes hung on the outside of a vehicle will get really filthy unless
completely contained in a soft zippered cover. The air blast will stuff
the chain and all other moving parts full of fine grit.
Front mount bike carriers are not uncommon. I see a few here and there.
Just make sure the lights are not blocked. If the bikes are not covered
the radiator airflow should not be reduced significantly.
Al Grayson