I have a JD LT150 bought brand new around 7 or 8 years ago. Never had a problem with it until now.
Tractor starts fine with the foot brake locked but when I let off the brake the engine stalls out. I can start the engine, then unplug the foot brake safety switch and I am able to let off the brake and move the mower which leads me to belive that it is some sort of safety switch issue..
Here are some symptoms:
Last fall (5 months ago) my stupid brother broke the front plastic bumper so I had the hood / cowl completely off to replace the broken plastic. At that time I may have disturbed some type of hood safety switch that I can not find.
I replaced the brake safety switch and the seat switch already (these were cheap so it wasn't a big deal)
I also looked for frayed / chafed wires under the hood and found none.
I might be able to give you assistance on rhis. There is no saftey switch that connects to the hood so your brother is off the hook. What I've seen more than once is the wires for the seat switch that go along the right fender support become frayed because of contact with brake linkage, belt ect. Take a look there and you might solve your problem. Good luck
Remember nobody ever complained about having too much horsepower!