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.


as of december 31 , 2017 , the aggregate future minimum payments under non-cancelable operating leases consist of the following ( in thousands ) : years ending december 31 . <table class='wikitable'><tr><td>1</td><td>2018</td><td>$ 9127</td></tr><tr><td>2</td><td>2019</td><td>8336</td></tr><tr><td>3</td><td>2020</td><td>8350</td></tr><tr><td>4</td><td>2021</td><td>7741</td></tr><tr><td>5</td><td>2022</td><td>7577</td></tr><tr><td>6</td><td>thereafter</td><td>9873</td></tr><tr><td>7</td><td>total minimum future lease payments</td><td>$ 51004</td></tr></table> rent expense for all operating leases amounted to $ 9.4 million , $ 8.1 million and $ 5.4 million for the years ended december 31 , 2017 , 2016 and 2015 , respectively . financing obligation 2014build-to-suit lease in august 2012 , we executed a lease for a building then under construction in santa clara , california to serve as our headquarters . the lease term is 120 months and commenced in august 2013 . based on the terms of the lease agreement and due to our involvement in certain aspects of the construction , we were deemed the owner of the building ( for accounting purposes only ) during the construction period . upon completion of construction in 2013 , we concluded that we had forms of continued economic involvement in the facility , and therefore did not meet with the provisions for sale-leaseback accounting . we continue to maintain involvement in the property post construction and lack transferability of the risks and rewards of ownership , due to our required maintenance of a $ 4.0 million letter of credit , in addition to our ability and option to sublease our portion of the leased building for fees substantially higher than our base rate . therefore , the lease is accounted for as a financing obligation and lease payments will be attributed to ( 1 ) a reduction of the principal financing obligation ; ( 2 ) imputed interest expense ; and ( 3 ) land lease expense , representing an imputed cost to lease the underlying land of the building . at the conclusion of the initial lease term , we will de-recognize both the net book values of the asset and the remaining financing obligation . as of december 31 , 2017 and 2016 , we have recorded assets of $ 53.4 million , representing the total costs of the building and improvements incurred , including the costs paid by the lessor ( the legal owner of the building ) and additional improvement costs paid by us , and a corresponding financing obligation of $ 39.6 million and $ 41.2 million , respectively . as of december 31 , 2017 , $ 1.9 million and $ 37.7 million were recorded as short-term and long-term financing obligations , respectively . land lease expense under our lease financing obligation amounted to $ 1.3 million for each of the years ended december 31 , 2017 , 2016 and 2015 respectively. .
Question: what was the rent expense for all operating leases in 2017, in millions?
Answer: 9.4
Question: and what was it in 2016, also in millions?
Answer: 8.1
Question: what is, then, in millions, the total rent expense in both of those years?
Answer: 17.5
Question: what was the rent expense for all operating leases in 2015, in millions?

5.4