Yes it would work.
A Pokémon with Poison Heal with will gain 1/8 of their maximum HP back at the end of every turn if the Pokémon is poisoned or badly poisoned. The Toxic Orb inflicts the holder with the badly poisoned ailment after one turn of battle so unless you have a Pokémon with Heal Bell or Aromatherapy you will not need it again.
Leftovers restores 1/16 of the Pokémon's maximum HP (rounded down) each turn when held.
There's only one problem with this no Pokémon with Poison Heal can learn Trick or Switcheroo as only Shroomish, Breloom and Gliscor have that Ability. So it would only work if one of your other Pokémon used it on you in a Double or Triple Battle or your opponent used it on you which in that case is highly unlikely.
Nevertheless if you did have your other Pokémon use Trick or Switcheroo or your opponent did use it on you to give you Leftovers, (after the Toxic Orb had activated of course and give you the badly poisoned ailment) you would be recovering 3/16 of your maximum HP back per turn.
Sources: Poison Heal, Toxic Orb, Leftovers, Trick, Switcheroo
Hope I helped :)