I repaired a 9.9 Merc that uses the same ignition module that’s on the 15 you have a couple years ago – someone at this site gave me a simple Ohm-meter procedure for checking out the module and it quickly showed me it was bad – I can’t find what I did with that procedure – maybe someone will post it for you. I remember replacing it with an aftermarket Mallory module I found online that was a lot cheaper than Mercury or Sierra. Mallory is a very respected name in performance automobile ignition systems.
Your problem could be the module, or the stator that’s under the flywheel.
Dave

Hey – I found that I had saved the test procedure in my computer – here’s copy and paste of it below:
Dave

I’ll bet it’s the switchbox. Hopefully the stator is still ok after you turned the motor over with the leads disconnected.
Test the trigger (brown/white and brown/yellow leads) between the leads with ohmeter at Rx100 scale. Should read 6.5-8.5.
Test the stator (black/white and black/yellow leads)
first test stator plate to ground, reading should be 0. You may or may not have a black ground wire from the plate to block, some used the stator base as a ground to block. Test between the black/white lead and ground with ohmeter at Rx10 scale, should be 12-18. Test between black/yellow and ground, meter at Rx1000 scale, should read 3.2-3.8. Test between black/yellow and black/white leads, meter at Rx1000 scale, should be 3.1-3.7.

You can test the switchbox by using jumpers and reversing the stator leads and trigger leads before the switchbox. If the no spark moves to the other cylinder, it’s the switchbox