"The bigger they are..." Shove to prone
athletics 1d20+15 : 13 + 15, total 28
Grapple
athletics 1d20+15 : 3 + 15, total 18
"the harder they fall!" Flurry of blows (ignore advantage if you were not knocked prone)
unarmed attack 1d20+10 : 15 + 10, total 25
unarmed attack adv 1d20+10 : 12 + 10, total 22
bludgeoning damage 1d8+5 : 2 + 5, total 7
unarmed attack 1d20+10 : 16 + 10, total 26
unarmed attack adv 1d20+10 : 8 + 10, total 18
bludgeoning damage 1d8+5 : 4 + 5, total 9
If either hit, roll con save DC 16 vs stunning strike.