To me it sounded like he wanted to pick more than 15 lights...like 45 for a 36".
OK. I thought the radio buttons would not let him select the longer fixture options. For all fixture lengths, you pick any combination of 15 LEDs for a 12" PCB, and we build those boards end-to-end for longer fixtures.
Yes, that's what I thought you could do, because it says in step 1 choose the fixture length. I see I misread the instructions.