I am sorry titi. I have been there
I am not a vet but I think every 15 minutes is too much if this is like a rehydation fluid. The babies are getting no chance to rest and sleep.
It is very easy to drown such tiny pups when giving them fluids. You could use an artist paintbrush and drop the fluid in or you can use a tiny syringe. You need to go very slow, drop by drop.
I think to be honest that they have bloat and it is very difficult to pull them through this. The falling is a symptom. They may have gas in the bowel and this is making it hard for them to move without pain.
You are doing all you can sweetie and giving them the only chance they have. You may lose them all but you may keep the one pup that seems healthy as he is a fighter.
Hugs to you