Who can beat the 15 pirates that Dooku couldn’t beat?

Round 1: No lightsabers.
Round 2: Lightsabers only.

Nobody can imo

HK-47. He blasts the irritating meatbags away

Nobody.

The Ones, Yoda, Mace, Luke, Anakin, etc. The "Dooku not being to beat them" is honestly just nonsense. We've seen Jedi and Sith be surrounded by enemies and use acrobatics and the Force to survive them. Now fair enough that Dooku doesn't do jumps and twirls much, but anyone Maul tier and up could theoretically do it.

Vader.

He has taken down 128 Imperial Storm Troopers by himself.

No one. Not even The Son could hold up against such deadly enemies.

S6 Dooku

As entertaining as the meme of Dooku being captured by 15 pirates is, I really need to address something.

By my rough count, there were at least 28 pirates (the featurette for Dooku Captured has Filoni state 30) surrounding Dooku on all sides. Not to mention all the pirates that were inside Hondo's base, plus all the pirates still onboard Hondo's ship. Dooku was also unarmed at the time. Couple that with the lower levels of power we see in Canon than in most of Legends (making Canon more in line with what we see in the movies), and it's sort of a no-brainer why Dooku chose to surrender. 

All that said, give the character a lightsaber, and the situation changes. 30 foes at once, surrounding the character on all sides, is a pretty tall order, but a ton of Legends characters could easily pull it off. I'd even argue several Canon characters could do the same. Yoda, Mace, Anakin, Obi-Wan, Starkiller, Revan, The Exile, and RotJ Luke, just to name a few.

HoU might beat them

Tiin and Kolar laugh in the faces of these amateurs