Snorlax - Worth keeping?

I would say it depends. ZH/E is decent. Its still a Snorlax. I think the lvl 30 with L/HB is fairly bad because of its IV. If you need a defender right now then power the ZH/E, otherwise wait till you get the prefered moveset.

Great catch, contrats!

keep it and use it.
maybe find it a nice gym to hang out in.

You can use the L HB Snorlax to attack, without power up, it's at 30.

Z E is fine in defense, and the difference beetween 0 and 15 in attack stat is huge!
You can power it up,if IVs are really good (especially att 15)

I have a L/HB lax and it is an excellent generalist attacker. It will never see the inside of a gym for that reason. (I made that mistake once and didn't have him for 3 months). The fact that he is already at L30 makes up for his poor IV. He will tear up almost anything.

That is a nice Snorlax for attacking. I attack with Blisseys, so he will still have a better attack then they do.

Level 30 L/HB - Good for attack - but don't put any candies into it.

ZH/E is not too bad for defense and if you want you could power it up.

In gameplay, there is not much difference between an IV attack of 0 and 15. Usually, your quick move damage will be the same, and your charge move is increased by a few points of damage. Nothing too significant.

Your moveset will matter more - a Snorlax with 0 attack IV but Lick + Hyperbeam will do much more damage than the worst attacking moveset - Zen Headbutt + Earthquake, with 15 attack IV. It'll be a great generalist attacker. Bit on the slower side of things, but other than against Blissey, it'll still take down multiple Pokemon before fainting despite the low IVs, so don't worry too much about them.

Since the Z/E Snorlax is your only good one, if you've got candies you may as well spend them on it and place it in gyms. Yes Earthquake is a mediocre move in comparison to the others, but it's not terrible.

Anyway, your defender is only one of ten in a gym, so one suboptimal moveset isn't that big of a difference. If a gym falls with your Snorlax in it, it won't be because your Snorlax has Earthquake instead of a better move. Don't feel like you're hurting the gym by putting it in. It's still a better defender than most Pokemon with their best movesets.