Please answer the given financial question based on the context.
Context: united parcel service , inc . and subsidiaries notes to consolidated financial statements 8.375% ( 8.375 % ) debentures the 8.375% ( 8.375 % ) debentures consist of two separate tranches , as follows : 2022 $ 276 million of the debentures have a maturity of april 1 , 2030 . these debentures have an 8.375% ( 8.375 % ) interest rate until april 1 , 2020 , and , thereafter , the interest rate will be 7.62% ( 7.62 % ) for the final 10 years . these debentures are redeemable in whole or in part at our option at any time . the redemption price is equal to the greater of 100% ( 100 % ) of the principal amount and accrued interest , or the sum of the present values of the remaining scheduled payout of principal and interest thereon discounted to the date of redemption ( at a benchmark treasury yield plus five basis points ) plus accrued interest . 2022 $ 424 million of the debentures have a maturity of april 1 , 2020 . these debentures are not subject to redemption prior to maturity . interest is payable semiannually in april and october for both tranches and neither tranche is subject to sinking fund requirements . we subsequently entered into interest rate swaps on the 2020 debentures , which effectively converted the fixed interest rates on the debentures to variable libor-based interest rates . the average interest rate payable on the 2020 debentures , including the impact of the interest rate swaps , for 2016 and 2015 was 5.43% ( 5.43 % ) and 5.04% ( 5.04 % ) , respectively . floating rate senior notes the floating rate senior notes bear interest at either one or three-month libor , less a spread ranging from 30 to 45 basis points . the average interest rate for 2016 and 2015 was 0.21% ( 0.21 % ) and 0.01% ( 0.01 % ) , respectively . these notes are callable at various times after 30 years at a stated percentage of par value , and putable by the note holders at various times after 10 years at a stated percentage of par value . the notes have maturities ranging from 2049 through 2066 . in march , june and august 2016 , we issued floating rate senior notes in principal balances of $ 118 , $ 74 and $ 35 million , respectively . these notes bear interest at three-month libor less 30 basis points and mature in 2066 . capital lease obligations we have certain property , plant and equipment subject to capital leases . some of the obligations associated with these capital leases have been legally defeased . the recorded value of our property , plant and equipment subject to capital leases is as follows as of december 31 ( in millions ) : .
||2016|2015|
|vehicles|$ 68|$ 74|
|aircraft|2291|2289|
|buildings|190|207|
|accumulated amortization|-896 ( 896 )|-849 ( 849 )|
|property plant and equipment subject to capital leases|$ 1653|$ 1721|
these capital lease obligations have principal payments due at various dates from 2017 through 3005. .
Question: what was the change in millions of vehicles from 2015 to 2016?


Answer: The answer is:-6.0