1996 mazda protege wont start in the cold!!?

k, i got a 96 mazda protege 5 speed with a 1.5L... now only when its really cold out it literally take 15 mins to start, the battery turns the engine over but i have to hold the gas in for like 15 mins while turning it to even get it to start.. but once its running its fine, and i also cant let it sit for more then 2 hours or itll take forever to start again... heres the things i got done to it. new plugs wires cap airfilter, fuel filter sumwhat new, pcv, oil change with 10-30,.. what can it be???