You would usually read this as "one point five years." 0.186 years would be read as "oh point one eight six years."
In a special case where we recognize the decimal as a commonly-occuring fraction, we might read it that way: "one-and-a-half years."
I was about to say that we only use "year" for the exact period of one year. " That isn't quite true because we also say "half a year," and "a quarter of a year." I could invent a rule for this, but I won't.
As other have noted, In the US we use commas to group thousands, and decimals to separate the whole part from the decimal fraction: $1,234,567.89; so your number would be written as "1.5 years."