Wrathamon
Adventurer
15 minutes presumes prior knowledge of how many h.p. it has, which might not be the "mere" 600+ you expect. As I mentioned before, it could legitimately, by-the-book have 900+ h.p.
With regards to the Tarasque not having the ability to throw objects listed in its stat block, that's because it is an implicit, improvised action which the rules allow ANYONE with appropriate limbs to take. Listing every damn thing a creature could do in its stat block would needlessly eat up page after page of the Monster Manual, just to fend off people who make arguments of this sort. Arguing that the Tarasque can't throw rocks because it's not listed in its stat block is like a DM arguing that your PC can't breathe because nowhere on your Character sheet does it specify that you can. Any monster or PC can take any action that would be physically plausible given that creature's anatomy and ability scores (i.e. a Pixie couldn't throw a huge rock, because it's not strong enough, not because rock throwing isn't listed in the Pixie stat block.)
Now, can the tarasque throw that rock AS WELL as a giant could? Probably not, since giants specialize in that kind of attack and for them it's not an improvised action. How well the Tarasque throws the rock depends on its Dexterity score. So it might not hit the Wizard right away, but it certainly can try!
Maybe the next Monster Manual need to have a page right at the front that says, in bold letters:
"ATTENTION RULES LAWYERS! ALL MONSTERS IN THIS BOOK POSSESS THE ABILITY TO TAKE INPROVISED ACTIONS NOT LISTED IN THEIR STAT BLOCKS. THE ABILITIES PROVIDED IN THE STAT BLOCKS REPRESENT TYPICAL ACTIONS TAKEN BY THE CREATURES, NOT AN EXHAUSTIVE LISTING OF EVERYTHING THE CREATURES CAN DO. HAVING THE MONSTER DO SOMETHING DIFFERENT IS 100% LEGAL AND LEGITIMATE PROVIDED THE ACTION IS WITHIN THE CREATURE'S PHYSICAL CAPACITY."
But, some are claiming that it is too stupid to know to pick up a rock and throw it. Which is debatable and a legit argument. But, that is saying "throwing a rock" instead of describing it has flinging a spray of debris (dirt, rocks, plants) which even dumb animals can do when overly frustrated.