I can only fill the gas tank very, very slowly. 15 minutes does not fill the tank. This just started happening this week. What ever would cause this?

Use this boards search feature to view dozens of threads on this subject. Type “slow fill” into the search box…

Also google “anti-spill roll-over check valve”

It partly depends on the car. Many cars have stickers warning you not to top off the tank. If you insist on topping off the tank on one of those cars, it is going to do exactly what you are finding. That check valve Caddyman noted, is a good chance.