Read the following texts and table with financial data from an S&P 500 earnings report carefully.Based on the question-answer history (if provided), answer the last question. The answer may require mathematical calculation based on the data provided.


item 1b . unresolved staff comments not applicable . item 2 . properties our global headquarters are located in chicago , illinois , at 20 south wacker drive . the following is a description of our key locations and facilities . location primary use owned/leased lease expiration approximate size ( in square feet ) ( 1 ) 20 south wacker drive chicago , illinois global headquarters and office space leased 2032 ( 2 ) 512000 141 west jackson chicago , illinois trading floor and office space leased 2027 ( 3 ) 150000 333 s . lasalle chicago , illinois trading floor and office space owned n/a 300000 550 west washington chicago , illinois office space leased 2023 250000 one north end new york , new york trading floor and office space leased 2028 ( 4 ) 240000 . <table class='wikitable'><tr><td>1</td><td>location</td><td>primary use</td><td>owned/leased</td><td>lease expiration</td><td>approximate size ( in square feet ) ( 1 )</td></tr><tr><td>2</td><td>20 south wacker drive chicago illinois</td><td>global headquarters and office space</td><td>leased</td><td>2032 ( 2 )</td><td>512000</td></tr><tr><td>3</td><td>141 west jacksonchicago illinois</td><td>trading floor and office space</td><td>leased</td><td>2027 ( 3 )</td><td>150000</td></tr><tr><td>4</td><td>333 s . lasallechicago illinois</td><td>trading floor and office space</td><td>owned</td><td>n/a</td><td>300000</td></tr><tr><td>5</td><td>550 west washingtonchicago illinois</td><td>office space</td><td>leased</td><td>2023</td><td>250000</td></tr><tr><td>6</td><td>one north endnew york new york</td><td>trading floor and office space</td><td>leased</td><td>2028 ( 4 )</td><td>240000</td></tr><tr><td>7</td><td>one new change london</td><td>office space</td><td>leased</td><td>2026</td><td>58000</td></tr><tr><td>8</td><td>data center 3chicagoland area</td><td>business continuity and co-location</td><td>leased</td><td>2031 ( 5 )</td><td>83000</td></tr><tr><td>9</td><td>bagmane tech park bangalore india</td><td>office space</td><td>leased</td><td>2020 ( 6 )</td><td>72000</td></tr></table> data center 3 chicagoland area business continuity and co-location leased 2031 ( 5 ) 83000 bagmane tech park bangalore , office space leased 2020 ( 6 ) 72000 ( 1 ) size represents the amount of space leased or owned by us unless otherwise noted . ( 2 ) the initial lease expires in 2032 with two consecutive options to extend the term for five years each . ( 3 ) the initial lease expires in 2027 and contains options to extend the term and expand the premises . ( 4 ) the initial lease expires in 2028 and contains options to extend the term and expand the premises . in 2019 , the premises will be reduced to 225000 square feet . ( 5 ) in march 2016 , the company sold its datacenter in the chicago area for $ 130.0 million . at the time of the sale , the company leased back a portion of the property . ( 6 ) the initial lease expires in 2020 and contains an option to extend the term as well as an option to terminate early . item 3 . legal proceedings see 201clegal and regulatory matters 201d in note 12 . contingencies to the consolidated financial statements beginning on page 87 for cme group 2019s legal proceedings disclosure which is incorporated herein by reference . item 4 . mine safety disclosures not applicable. .
Question: what square footage will the one north end ny, ny premises be reduced to in 2019?
Answer: 225000.0
Question: and what is the starting square footage?
Answer: 240000.0
Question: so by how much will the square footage decrease?

-15000.0