Granny would like to chime in: I don't know a thing about tires, but...
Put your cell phone in that bag, too, and phone-a-friend, or someone--as a last resort, call the cops and ask their advice on who to call if you can't reach anyone else-- to come pick you up if all the spare tubes get flats and it's a very long walk. You can put the bike in the trunk well enough to get back home. You will not be biking on Mars. LOL
That 15 mile walk would take the wind out of most people's sails for awhile. I'd say get the tires you want, charge the cell, and go enjoy!
I just bought a bike today, after decades of not riding. I'm about to get foolish enough to venture out of the yard.
You'll be fine.