Case Vaporeon
I have 20 + 80 IV vapo. but I found this Att 15 def 15 hp 6 lvl 30. should I power it up to 38. 38 is the break-point where you make 5 damage at tyra raid. It is huge step 4 to 5. 20 % more damage. If it have 15 defence the hp is quite meaningless. 600 candy and 400 k st.
Answers
Like others have said, Machamp is much more useful for Tyranitar.
But if you're also wondering if this Vaporeon is worth powering for other bosses, it is, since it's got 15 attack and defence which are more beneficial on Vaporeon than stamina, since Vaporeon's stamina is already really high and it's attack and defence are the lower of it's 3 stats. When maxed out it'll have 208 HP instead of 215, which is still incredibly high.
As the others stated, Machamps are strictly better in tyranitar raids, but one should not forget that a high level vaporeon is so much more than just a tyranitar counter: with hydropump, he is also viable in arcanine solos and he is useful against all of the fire legendaries as well.
So if tyranitar raids is not all you are interested in and you do not have a high level vape yet, I for one would advise to power him up.