Yes, there is. Even boiling it down to an estimate against a similar benchmark I've worked on - Keepmoat Stadium.There is no way it could be built in 15 months
The 15k stadium, adjacent athletics facility and 500 seater grandstand, multiple levels of fit-out (including a gym) and significant landscaping took around 14 months.
The only stadia which will take more than 12 months to substantially complete are behemoths such as Spurs or Wembley.
I've got more examples than I could possibly quote on here from my 16 years and counting in the industry. Happy to share if you are that bored.
For me, the biggest headache at FF is still the scale of ground prep required to even get started.