Recently, the need came up to express "one and a half year ago".

Perhaps, the "safest" way to go, would be {wa'maH chorgh wen} "18 months ago".

But I'm wondering whether it would be acceptable as well to say, {wa'
wa' bID je ben} for "one and a half year ago", or maybe even {wa' vI'
vagh ben} for "1.5 years ago".

Possibly wa' wa' bID je ben, or maybe it would be wa' bID je ben. Possibly wa' ben jav wen je. wa' vI' vagh ben certainly works.

As for whether these are "acceptable" to a Klingon, we don't know.

-- 
SuStel
http://trimboli.name