The questions

1 What is celebrated, mathematically, on 14 March and 22 July?
2 Which form of Chinese originated in Guangzhou?
3 Summoner’s Rift is the main battleground in what game?
4 What is advertised as “Scotland’s other national drink”?
5 Which archipelago is home to Norway’s polar bears?
6 Which activist was arrested in Rochester, NY, in 1872 for voting?
7 What was the first martial art to become an Olympic sport?
8 Which organ produces insulin?
What links:
9 Dominic McLaughlin; Jamie Parker; Daniel Radcliffe?
10 Riviera’s second city; goddess of victory; Bill Bowerman and Phil Knight?
11 Star patterns; time travel in Hill Valley; piano; neo-Nazi code?
12 Lime Rickey; Arnold Palmer; Shirley Temple; Virgin Mary?
13 Political Wife (Sarah Vine); Politician (Rory Stewart) Professional Footballer (Paul Merson); Boy (Robert Webb)?
14 Ghost; Lordi; Pussy Riot; Sleep Token; Slipknot?
15 Ancelotti; Enrique; Guardiola; Happel; Heynckes; Hitzfeld; Mourinho?

The answers

1 Pi (3/14 and 22/7).
2 Cantonese (from former name).
3 League of Legends.
4 Irn-Bru.
5 Svalbard (Spitsbergen).
6 Susan B Anthony (and 14 others).
7 Judo (1964).
8 Pancreas.
9 Played Harry Potter on stage and screen: forthcoming HBO series; original cast of HP and the Cursed Child; film series.
10 Nike: Nice, named after Nike; in Greek myth; founded Nike trainers.
11 88: 88 constellations recognised by the International Astronomical Union; DeLorean’s 88mph in Back to the Future; 88 keys; numerical code for “Heil Hitler”.
12 Mocktails.
13 How Not to be a … books.
14 Masked rock bands.
15 Managed two clubs to win European Cup/Champions League.