PvP Power Up

Gonna echo some of the other sentiments you'll hear and say wait and see. You'll only be able to bring that Tyranitar to level 13.5 to stay below the 1500cp cap.

You could hold off on any decision to commit resources until we know more about PvP.

I see no advantage in making decisions and spending resources ahead of time...only an opportunity to waste dust/candy

PvP will focus more on TDO than DPS, thus TTar will still be better suited for the ulimited CP category. Other rock/dark mons will have a much higher TDO since they can be much higher levels while maintaining a lower CP than TTar. Umbreon in Dark and even Regirock in rock types for example, would both be better options for 1500.

The master league is going to be about Max IV pokemon at level 40, and even there, only the strongest ones will be competitive. Tyranitar is likely one of those, although the double weakness to fighting may be critical, just like Moltres's double weakness to rock could be fatal.

If it's IVs fall very close to 1500 (or 2500) when you power it up, it could play well in those leagues, but I suspect even better would be a pokemon with IVs that optimize the total stats. For Ttar, that is likely a zero attack, and some combination of (d/s) 15/0, 15/15, or 0/15, or values very near those that fall at or just below 1500 CP and 2500 CP.

Tyranitar is not good 2500cp and especially not 1500cp.

Obviously wait and see, but this seems to be a candidate for the master League (not to mention it will then be useful in raids too!).

The great League and ultra League probably won't be great for the ultra-high max cp Pokemon, since they're high CP due to competitive attack stats. Lower CP leagues will be optimized with tdo options that have low attack stats for the CP.

Id say that Ttar is unlikely to be a good choice in PvP in general. Firstly, it has a double weakness. Secondly, it doesnt have the correct stat shape for Great and Ultra league. Master League it will have some utility though. Might even be quite strong as it counters Mewtwo and Rayquaza while having a better stat shape than either of them.

TTar's stats wont be any worse at those CPs than other mon's with the same CP its just that the stat shape isnt ideal (too much atk) while carrying a double weakness.

Of the two lower leagues it would work best in Ultra League as Umbreon would be superior in Great League.

My advice: Max it out. Will always be great for raiding and a maxed out TTar might serve some purpose in Ultra League since Machamp doesn't exactly have an ideal stat shape and is quite weak against most Master Mons.