Replace blood with twice the volume of jello fix pressure

(Good luck that all sucks)

Aspirated: Has a puff of air on it. Most noticeable at the beginning of a word (hold your hand or piece of paper and say "testing" to get aspirated and unaspirated t)

Disclaimer I don't have a great story why fifteen sounds ok unaspirated besides the f. But mumbling fif-deen certainly sounds better than thir-deen to me.

The ones with an r or n before have the chance to be a more different sound for a lot of speakers (a flap more like in ladder). So the consonant of thirty or ninety is usually a bit more different from thirteen and nineteen.

In American English the t in fifty will usually be unaspirated (which sounds like a d to speakers in isolation). Fifteen is usually aspirated if spoken in isolation (probably what you think of as a true t) but I think that gets kinda lost in the f and less emphasized form in rapid speech.