I think very few single tour guys are hitting 1500 hrs.
What
@FLGUY and
@PMPT said about 750 hours for military-trained pilots. The FAA ATP total flight time requirement is a tiered model, depending on where you got your pilot ratings (more or less that's mil, aviation college, or mom and pop learn to fly). If you have less than those 1500 hours but you got your training from one of the better tiers then you are eligible for a restricted ATP. Practically speaking that restriction means you can be a first officer on an airliner but not a captain, which is actually a moot point because the hour requirement for anybody to be a captain (regional or major) is much higher. The restriction is annotated on your pilot certificate and it gets removed after you get more hours and fill out the paperwork to get it taken off.
Like anything, you can find a few strange situations and maybe loopholes. You could theoretically take a freshly winged mil guy or gal, which these days is about 200 hours, let's say they don't fly at all after winging (med, DOR, BUPERS screws them with an IA and staff duty instead of the RAG and a fleet tour, this is just a thought experiment). The person fleshes out the rest of those 750 hours in gliders, powered parachutes, hot air balloons, ultralights, they could still in theory be
legally eligible for a restricted ATP right at 750 hours- and get hired to fly regional jets if they pass the interview.
That's not going to happen in reality but that 750 hour gate (for mil dudes) can be higher than you might think. Ten years ago when I was in the HTs and flying with brand new IPs, a lot of them had only 700-800 hours of total time on their TH-57 initial NATOPS check paperwork. Everybody knows the saying feast or famine and back then it was definitely a famine. Oh, and it showed. The difference in SA between an 800 hour guy and a 1500 hour guy was noticeable- not quite a safety of flight kind of way but in a "here's a couple things to think about that will make you a better pilot" kind of way. When I moved over to primary instruction, the flight hours story of first fleet tour people from big wing and tacair communities also varied from a lot to a little bit; it wasn't just a helo community thing.
That's mostly food for thought. Either way, the bar for entry is still higher than a 250 hour wet commerical rating like the "old days" (before the Colgan crash). The regional training departments work with people from all sorts of backgrounds and for the most part they try to get everybody up to speed. Since the airlines are moneymaking businesses and sometimes they badly need to fill seats, that can mean training is a pump, not a filter. Other times they can afford to be very picky. (Sometimes that "pump, not a filter" description fits mil flight training too...)