If the thing has only run 3-4X in fifteen years and you've had a lot of rain but the well is only half full, it sounds as though you have great natural drainage and may not need a sump pump at all.
In your case, with the very limited running that you've seen, the deal pump you got should work just fine. It will indeed die of rust and old age before wear kills it.
I've gotten better life out of submersible pumps than pedistal pumps, but our sump pump may run quite frequently during periods where we see day after day of rain in the spring and fall.