I am have understood focusing on a single niche and single traffic choice will greatly increase you chances of succeeding in this industry.
I have chosen to go mobile but can't decide which of this two :
-Gaming
-Dating
Which is easier to learn and be profitable fast for a noob with a $1500 monthly budget..?
Your profitability speed depends on how fast you can optimize your campaign. if you can spend 500/day and keep a keen eye on your stats,cut down bad performers, you can see profit in 2-3 a days. but for this you need to know what and how much you need to test. i wouldn't suggest spending this high when starting out.
If you are starting out i wont recommend mobile. their are just too many factors to be optimized. It takes higher testing budget usually. adult dating or general dating is good start-up point. if you are keen on starting with mobile, then start with adult mobile dating. but for mobile, you need a good server + tracking available. imobitrax+dedicated server is preferred. u might get away with using high end vps, but make sure your vps is located in country you choose to run your offers. also many ppl recommend pof, but i have never ran pof traffic so cant say. Whatever you choose, stick to it, make it profitable and scale it.