You mention a LP powered forklift but the temperatures are not that cold and it should start a lot easier at 15F or -9C. I would suggest looking at your regulator as it likely has a wax build up inside it. Not sure how old this unit is but we see it pretty regularly here in Alberta. If it starts great after it has warmed up then that is likely the issue. The wax build up impedes the flow until after the unit warms up and the wax melts. A good test is to take a hair dryer to the regulator for a good while before cold starting. Get the regulator good and warm. Does it start fine? If so, that is your likely issue.