Turbo A15 engine will last a long time ... if you limit spark advance, and the engine runs rich enough. What follows is a starting point ... however after you set it up, you must
double check it to ensure there is no pinging* For street driving/highway driving, keep the stock vacuum advance (it will have no effect under heavy throttle or boost, but will give better throttle response and fuel economy off-boost and while speeding up and slowing down)
* Connect vacuum advance up directly to manifold. This will help idle and starting out under low throttle, but the vacuum advance will have no effect under heavier throttle
* Start with initial timing to 3 degree BTDC instead of the usual 5-7 degrees
* For 15 lbs boost, limit the mechanical advance to 23 degrees (stock for A14/A15 is 32 degrees). In the distributor, weld the advance slots partially to limit mechanical advance (see
Limiting Mechanical Advance)
Downside: On a forced-induction engine, the distributor advance won't be correct for varying boost levels. But you can set the advance for full boost ensuring safety, giving up HP and fuel economy for lower throttle conditions such as highway cruising. To get it perfect,
use an ignition controller instead of the stock distributor