Re: Bilge pump ?
like everything with boats, it depends, but probably. If the boat is moored, yes. If you cannot remove the plug easily from the inside, to run water out the boat, yes.
Some boats like whalers and carolina skiffs are sealed hulls and have no bilge below decks, and can be bailed out or are self-bailing; a bilge pump may be handy, but not necessary.
considering size alone, at 15' you are on the fence but if you have a bilge below deck, I'd get one. More important than size is how and where you use the boat.
I was thinking about this just yesterday after a big rain storm--back in the 60's/70's, growing up on the river, many if not most small boats didn't have them, and you just ran the water out after a storm or bailed. You could also ride around after a storm and often see at least one swamped boat, either no pump or dead battery.
Now pumps are better and cheaper, and batteries are better, so like many things, we boaters got along without, but life is better with.
Set up a seperate float switch, wired to the battery. get the kind that's in a box-like housing so something can't fall on topof it and keep it from running. A manual switch at the dash is convenient.