If the nail is in the sidewall, forget it.
If the nail in in the center tread, life is not so bad.
Don't ride with the nail in the tire. It will only make things worse. America tires have tubes, which in this case is a good thing. If you cannot get a new tube, get yourself a patch kit and get ready to do something riders use to do routinely, patch the tube. With a tubeless, I'd hesitate to ride a patch, and would absolutely not ride a plug longer than to the nearest shop. But with a tubed tire, you're at an advantage in this regard. Note carefully where the nail is, mark the tire. Take the wheel off, break down the tire, finding the hole in the tube should be easy enough, do a good job with patching the tube, reinstall everything, air it up and be on your way.
A good patch on a tube will last a long time. You don't have to worry about the integrity of the tire carcass, it will do fine on a cruiser.
Of course if you've never repaired a bike flat, grab a friend who has and knows how to do it. Growing up, every kid I knew had a Monkey Grip can handy, and was very adept at using it.
You'll hear horror stories that if you do this, you'll surely go to hell and burn with the rest of us demons who've used less than production quality parts. So use your own best judgement and if you doubt your ability and know of no one who you trust to do this but a bike shop, well there you go.
And yes the Green ones are faster, and they go longer, too!
That 15" wheel with the 90' tube stem is a bear! My $.02....Good luck.