When has the 10-year closed below 1.5% since 1962? Just a couple of compact lines of Julia will tell you.

dgs.jl

julia> using TimeSeries

julia> d = imfred("DGS10");

julia> d[v(d) .< 1.5]
6-element TimeStamp Array:
 2012-06-01  |  1.47
 2012-07-20  |  1.49
 2012-07-23  |  1.47
 2012-07-24  |  1.44
 2012-07-25  |  1.43
 2012-07-26  |  1.45

For a little comparison with R ...

>library(quantmod)
> d <- getSymbols("DGS10",src="FRED",auto.assign=FALSE)
> system.time(d[which(d<1.5),])
   user  system elapsed 
  0.001   0.001   0.020 

julia> @elapsed d[v(d) .< 1.5]
0.003257884

Not that anyone would do this on purpose mind you ...

> d[1,1]
           DGS10
1962-01-02  4.06
> d[1,1] = 1.23
> d[1,1]
           DGS10
1962-01-02  1.23

julia> d[1]
1962-01-02  |  4.06

julia> d[1].value = 1.23
ERROR: type TimeStamp is immutable