You have too many other interests to spend time mowing 15 acres.
Mow 1.5 or 2 acres of lawn around the house. Use the tractor you'll need to mow the rest with a 3 point mower, or hire a neighbor to mow that three or four times every year.
Otherwise mow with a 3 point finish mower on a tractor.
If there is a Husqvarna dealer nearby, go look at the home owner and commercial grade mowers. Compare the blade spindles and hydraulic motors. Compare the engine air filter housings. You'll want the commercial mower afterwards.
Whatever you buy make certain the blades are easy to remove for sharpening. You'll change them often enough. A Grasshopper zero turn raises the deck for access, others drop the blades and spindles straight down to slip out. Any deck you buy will be too heavy to lift with your arms and back, you'll need jacks or a hoist.