I have another thought , it seems your fuel pressure is adequate, but your complaint is long crank time. , so going by your description when you started thread I, over 15 minutes and crank time is long , indicates either fuel pressure regulator or voltage drop or low voltage . You've already replaced regulator , so we can pursue the fuel pressure bleed off or focus on original complaint, I'm going to look at your complaint . First things to do , remove battery cables, negative first , inspect for corrosion, especially positive cable spacer , if needed clean. small positive cable that runs across radiator support first then spacer and cable to starter and then negative. Next underhood fuse /relay panel , remove inspect for corrosion, clean if needed all fuses and relays. Start and either drive or warm to operating temp. Shut off and allow to set . Do this a few times to see if it improves.