Possibly replacing sand filter...???

As far as I can tell, my filter is about 15 years old and has never had the sand replaced. it is not working efficiently as I have to backwash weekly to keep the pressure low and has actually sprung a couple leaks in the plumbing between the pump motor to the filter (supposedly due to the high pressure?) Also, air is bubbling back into the pool after the equipment shuts off. Is this a bigger issue or does the sand need to be replaced? If I have a new filter installed, what's a realistic price? My pool is standard size -somewhere around 24*12 and 4-5 feet deep. Thanks!

Welcome to the forum.
Is this an above or in-ground pool? Asking because we need to know if the water level is above or below the equipment. In either case I don't understand how air could be bubbling back into the pool when the pump shuts off. Since you do have leaks I can understand how water in the pump and filter would drain back to an in-ground pool....gravity. As for sand causing problens I doubt it unless you added something to the pool that's gunking up the sand OR something has been damaged in the filter. Sand doesn't go bad even after 15 years. Mine is pushing 14 or so. What kind of pressures are you seeing right after backwash and just before backwash ?
Al