Power up snorlax with ZH/HS?

Depending on your local environment (whether gyms have a high turnover or not), 25XX might be enough for it to last a few hours. So powering it up might not be necessary.

I'd wait for a higher IV and use the current as is.

it s really good imo, I'd power him up.

I have a slightly worse iv one with L BS 5hp 13at 10df and I'm thinking of piwering him up, it s at 2493 lv 27

He is definitely worth taking to L30. Like blissey, snorlax, has a high base stamina. This makes stamina the least important IV for both.

Good defender.