Sandslash 100% IV

It won't make that deal on gyms, although I think it's fun to have some variety on both attacking and defending Pokémon. Sincerily, I don't think a Sandslash worth it. It may not be that difficult to got another better ground type pokemon, like Golem or Rhydon. But if you got many stardusts there, have fun. At least it's a 100%. It will worth alot in the future.

Personally, I probably wouldn't max him out but worth powering up a bit maybe. Depends on his current level.

I assume at level 15 it is just around 1000CP? If so, personally, I'd keep it for a prestige team. Certainly wouldn't use Sandslash as a defender since it has a weakness to water and grass. And tbh if you dodge well even at level 15 it can do some good damage to defenders that are weak against Ground moves.

Power him to level 30 only. He's a perfect IV mon, with the best attacking moveset, and Tier 3!

That's my current project. Powering up all the top attacking/defending mons per GamePress to at least 30.

No... Get a Rhydon

Mud Shot+Earthquake is a better attacking moveset than Mud Slap+Earthquake that other ground type pokemon can learn -- the shorter duration makes it easier to spam attack then stop and dodge -- but if you already have a Rhydon with Mud Slap+Earthquake above ~2200cp, just power that up and use it for fighting the occasional enemy fire, electric, or poison type. Rhydon has higher HP so he can afford to get hit a few times if you miss dodges. Instead of trying to dodge every quick move, I will usually attack three times and dodge every other quick move.

Save the Sandslash at a lower CP for training up friendly gyms.

100% ivs sounds nice but means nothing. Between a 100% and a 80% the CP difference can be +-60. (pure shit).
Buff him if you love the pokemon and you want to have something different, but i think there are like 50 Pokemon better to buff before him, +100 when the 2nd gen come.

He's very fast and does a decent amount of damage against the right Poke, but sadly his uses are few and far between.

He's an excellent counter to the Nido Royalty on the odd occasion you find them in gyms, and does well against Jolteon/Flareon.

I like him and if I had plenty of dust I'd power one up for occasional uses.

I like Sandslash a lot now since it has decent HPs and is great for prestiging. His CP is general lower too (like this one you got is < 1000) so it's useful if you don't have a very low CP Vaporeon (I don't).

Since he is a pure "ground" type, he doesn't take additional damage from ground attacks and takes less from rock attacks.

This makes him useful to prestige against Rhydon (very common now) and at times, Jolteon (not that common).

I wouldn't power him up though.