I think New Hyde Park would probably be your best bet. There is a morning train that leaves at 7:28 so figure 5-10 minutes driving/parking and that works perfectly with your ideal 7:15 departure. The train into Penn Station takes around 35 minutes and the 2/3 downtown (to the Park Place station) takes ~12....so figure about 50 minutes total with walking between stations and everything. Does that get you to work on time? There is a 7:09 train out of NHP too.
You could also take the LIRR to Brooklyn instead and take the 4/5 train into lower Manhattan, but it'll take the same exact amount of time and require a transfer at Jamaica. Going into Penn doesn't.
The only potential problem is parking. There are non-resident spots available at NHP, but I'm not sure how early they fill up. Best thing to do might be to take a drive by early on a weekday and check it out. Here's a map
that shows where public parking is located around the station. Blue is public, yellow is Village of NHP residents only. If you've gotta be in at 8AM, I'd recommend taking an even earlier train than the 7:09...sucks to be up that early, but you might have better luck finding a spot.