Sounds a lot like reflux,which is common in preemies. Breast milk is much more easily digested, so I wouldn't give that up. Also, while it may look and seem like a lot of milk coming up it typically isn't as much as it seems. The reason baby is hungry again soon after is because sucking keeps the reflux down, but it's a vicious circle because the milk increases the reflux. Alot of it has to do with their stomachs being small and squished up high. The stomach hasn't moved into it's proper place yet. Our daughter was NOT a happy refluxer. She also had a dairy/soy protein intolerance that caused severe gas, and pain and mucousy diarrhea. She screamed all the time until we got it sorted out with two kinds of medicine and prescription formula (I was having trouble making enough milk as it was, let alone cut more out of my diet). Rx formla was about $40 a canister, which has a double size scooper, so it was costing $80 for what a can of regular formula would sell for $8-$10. Insurance would not cover it.
You might try breastfeeding instead of bottle feeding. The amount and intake is more natural. Bottle can cause them to over-eat, which makes reflux worse, and if the nipple flow is too slow or too fast it can cause problems-they are either sucking too hard to get milk and intaking air, or milk comes to fast causing air intake. If baby's weight gain is ok, and there's no screaming or what seems to be pain, these things might help and baby will likely grow out of it. If there is pain and alot of fussing involved, or issues with weight gain, then you can talk to your pedi about medicine. A pacifier might help keep reflux down, as well as burping frequently, feeding smaller amounts more frequently, and keeping baby's head elevated or propped in a swing for 20-30 minutes after feeding, and being creful that there isn't any pressure on the tummy.
And of course, talking to your pedi is always reccomended if nothing else seems to work, or if you have concerns.