The cold starting procedure on the 150 (if my memory is correct) has you turning the prop over by hand while priming
This was a similar technique shown to me by the engineers of a very prominent UK school. They were required to start and warm 30 PA28 aircraft every morning throughout the cold mid winter. The technique was: set a piston at the top of compression and then using the accelerator pump give two strokes of the throttle and pull through. Do this for each cylinder plus two more for luck and start without delay. This worked every time; no flattened batteries, no flooded engines and no fires. I've done this successfully for over twenty years.
An engine fire is only a risk if you over prime. If you do not over prime then you will not have an engine fire, be it exhaust or carburettor, whatever starting technique you employ. If the engine is hot you probably do not need to prime. Never assume, in the first instance, that the fuel mixture is too lean but rather it is too rich.
A common reason for a difficulty when starting a warm engine is that the previous flight has not been shut down correctly. A common fault is to treat the mixture as if a switch. Rich to shut off; in a milli-second. Shut down with care allowing the engine to burn off all excess fuel and to leave the spark plugs clean