Not very slow. And slimes need lower taming /lore by the way.
First you need slime /snake stamina at 120 . You do it raising resist.
Cast paralyze fields in FEL with another account having 0 EvaInt . Run over them with slimes.
Or use Ortanord in TerMur to train all 5 (you will need to heal them)
While Slimes require lower Taming/Lore, they also have 1-5 Base Damage. Snakes have 1-4 Base Damage, so are slightly safer to use on a pet.
Yes, it's best to reach 120+ Stamina on them before you start training their Wrest up. You can do this with Spectral Spellbinders in New Haven. Once a pet maxes it's Resist skill, it's STR/DEX will skyrocket up to 125 if it keeps getting spammed with resistable spells. Doesn't take that long for a single pet (especially with the use of Whispering), but having to do it individually for 5 pets can take a couple hours.
It takes awhile to set up 5 Slimes/Snakes with 120+ Stamina/GM Wrest/GM Poison, but once you do have them, you can use them to quickly train another account's pets up to 120 Healing pretty fast, whether it's your own pets or a guildmate's. The more pets you train to 120 Healing with them, the more value and time saved you get by having these five Snakes/Slimes. So basically a high upfront time investment, that ends up saving you a lot more time in the long run, especially if you use them to train Healing on multiple pets.
I usually use a disarmed Gregorio for training Wrest/Tact on pets with low Wrest/Tact skills, then Discord the pets once their Wrest/Tact gets too high, and then they can start gaining Wrest/Tact again (oftentimes up to GM then). Gregorio is perfect for training Anatomy/Poison/Magic skills on too, due to his immunity to pet damage and when disarmed his low Wrest makes him easy to land hits on (he dishes out virtually no damage too when disarmed).
Another trick to training, is having an Archer in party running "Play the Odds" on cooldown to buff the pets. With 120 Archery/GM Tact/Lvl 3 Primer, Play the Odds will provide +45% HCI/+30% SSI to party (and their pets) for 60 seconds, with a 90 second cooldown (so 2/3 uptime). Pets will successfully land hits much more often due to the +45% HCI (and therefore get more chances to gain skill), and the +30% SSI will allow even sub-150 Stamina pets to reach max swing speed (once again accelerating the rate of skill gain). The +HCI/+SSI also helps counteract the debuffs from Discordance on your pet.