cg,

I wouldn't be worried about 1.5 seconds.

Start the car up again in a few days and see what happens.

Lifter noise sounds like ticking. knocking, on the other hand sounds like marbles in a tin can. It's loud, sounds terrible, and it means something is really wrong with your engine if it's happening at idle. 1.5 seconds is way too short for the noise to be piston slap, which usually only goes away when the engine warms up (if ever.)

Report back to us.