Ok first post on this problem .

Problem: engine dies after 15 mins. or so
Problem: haven't isolated the whats causing this.

Here's what I would do to isolate harness and ign. system .
Disconnect wires from + side of coil.
Run two wires from battery to + terminal on coil . one wire with an in line ballast resistor . start car and remove solid wire so you don't cook the coil
if the engine still dies, you have very little wireing and parts to look at ........
I would unhook your alt. just for the test .

Now if the engine still dies , your down to coil, ecm , dist and carb/fuel .
see what happens .