Our 41 year old home has the old “5 Gallon Flush” toilet. I replaced a leaking flap valve with the new adjustable flush type.
It works great! Most of the time, the partial tank, reduced setting works just fine. If I notice a few “Bitter Clingers” circling the drain, I just hold the lever down to finish the complete flush.
Less than $5 at Lowe’s/Home Depot.
If I had to flush 15 times I would probably give-up after 7 and think it is someone else’s problem.