Open the doors and see how wide the car is can you get out if not the answer is no.

Unfortunately it’s not my current home and the garage in question is occupied but I will measure the width of the car with doors open.

You've already answered your question in your initial post... A 6' x 15' car is 5' smaller than your 11' x 20' garage in both length and width. Unless I'm missing something here, it's just a simple math problem. You'll have to contend with space for opening doors and getting around your steps, but the car will definitely fit without other obstructions.

As long as no one wants to get in or out of the car so maybe push it in and pushit out.