I would hold off spending resources on a Heatran for now. It's not relevant for any of the current raids, and it might even get a 3 hour raid day where it receives a better charge move in the future. Maybe not this year, but Moltres, Charizard and the upcoming BB Blaziken should do fine until then for my case at least.
Heatran
Is Heatran worth investing into, maybe not maxing out, but at least getting it as close to 2500 without going over?
I know it's the bulkiest fire attacker in the game right now, but I also saw that it's movesets aren't that great either.
I just thought that it's 10 resistances might make it a useful pokemon that could be worth a little investment.
Answers
If this happens at all, keep in mind all the legendaries that have been released before it and that even the Beast trio haven't had their raid days yet. It really does deserve a better charge move though.
Sadly Heatran is a bit of a novelty these days, unless you're willing to max one out for the sole purpose of PvP Master League, where it does generally perform well against anything not Ground type and have some great matchups. There are other good options that doesn't require rare candy though.
It really isn't very expensive to power up a Heatran for ultra league. If caught at level 20, it will take about 7-8 power ups, to get it as close as possible to 2500. That's 19-22 candies, and 20K-23K stardust. If you like Heatran and want to try it out, why not?
Stone Edge seems to be it's best charge move in PvP. I have one with 7/15/15 IV's (traded), at CP 2497, with FS/SE, and I've been pretty successful with it, but that has a lot to do with what opponents it happens to face.