15-15-10 89% Ttar, shall I power it up?

Moveset?

If you've got dust and candy to burn, sure. Tyranitar is going to be useful whether its IV is 89% or 98%.
Plus with raids you can always get yourself more Larvitar candy, rare candy, and TMs to get that ideal moveset.

You just need to make one extra dodge to compensate for the slightly lower HP.

I got lucky with a hatch (before raids), then two raid catches with very high IVs, but now that I've leveled-up those three, my next one is probably an 89-percenter, and I feel OK about that.

As my collection of mediocre Moltres shows, there's no guarantee you'll get a better IV mon in a raid. It's the luck of the draw each time. So, if you've got the candy to make this guy a viable attacker, he'll perform well for you. If your current candy/dust situation is such that you can't get him at a high enough level to be of use, then you could keep saving. But you can never have too many Tyranitars, so hit him with the dust!

I would say absolutely yes. That is a fine TTar once you TM away the bad moveset.

I powered up a tyranitar of 10a12d14s to L30 and it serves me well. Period.

I think I would hold off. How many better you got? How bad do you need it?

That's better IV than my best T-tar, and I have two at level 30. Go for it!