下面这段SQL语句在Rstudio里执行的时候报了条件语句格式的问题，尝试更改更格式还是不行，求教各位，感谢！
SELECT
YEAR(PaymentDate) as year,
MONTH(PaymentDate) as month,
cast(sum(SalesTotalPrice*CurrencyToUSDRate) as DECIMAL(12,2)) as sale
FROM
HofanDW_DW_History.dbo.FactOrderDetail2_History
GROUP BY
MONTH(PaymentDate),YEAR(PaymentDate)
UNION
SELECT
YEAR(PaymentDate) as year,
MONTH(PaymentDate) as month,
cast(sum(SalesTotalPrice*CurrencyToUSDRate) as DECIMAL(12,2)) as sale
FROM
FactOrderDetail2
WHERE
YEAR(PaymentDate)>='2015'
GROUP BY
MONTH(PaymentDate),YEAR(PaymentDate)
ORDER BY
YEAR(PaymentDate),MONTH(PaymentDate)

报错内容
Error: unexpected numeric constant in:
"                FactOrderDetail2
YEAR(PaymentDate) >= '2015"