A1-15 is the fuel line you need to use for lines that always have fuel in them, like the line from the fuel tank to the engine or filter.
A2 or A1 fuel line should be used for lines that aren’t full of fuel all the time, like the tank fill and tank vent lines.
Do your fuel lines need to be replaced? That depends on a few variables. It’s a lot like the discussions about fogging and/or using anti-freeze when you store the boat. The conditions that the boat is stored and used in make a big difference. Also where you buy your fuel can have a big effect because of where different refiners get the base stock that is used to make your fuel and many different chemicals are added or removed from the crude oil they start with depending on that and where the fuel is going to be sold.
Next is how fuel lines fail, as
scoflaw correctly points out. Fuel line start failing first on the inside and little pieces will fall off and plug things up. This probably isn’t a big concern of yours, because carburetors are a lot more tolerant of these little pieces than fuel injected engines and the filter will catch some of it.
Next step is they will start to allow air to be sucked in (because air molecules are much smaller than fuel molecules) once again not as big a deal for carbs because they can get rid of the air much easier than a system like the MerCruiser cool fuel 2.
The next step is they start to leak, and that can be really bad. It’s very important to not let them get to that point.
It shocks me that some of the people on this board have fuel lines from the 70’s. They must have much better conditions and/or fuel then we have here in Minnesota. The fuel lines made in the 70’s weren’t designed to handle alcohol and have all been replaced. I have replaced many bad fuel lines on boats as new as the early 2000s. My brother has a 1996 boat that the lines are starting to get stiff and will get replaced this spring if he decides to “keep it one more year”.
When the manufacturer say’s that their life is 10 years, what they are really saying is that they should last at least 10 years and may last longer.
I recommend you listen to somebody knowledgeable who has actually seen your fuel lines rather then us internet guys.