A few questions here in the middle of the summer...
What bike are you riding? Air-cooled, liquid-cooled, V-Twin, four-cylinder, etc
What ambient temperature are you starting the motorcycle at that 15w40 is causing hard starting? Looks like you are in California. As in the bike won't start and experiences difficulty to get going at all?
With that said T5 is still a 15w40, despite the creative math.