Looks this behavior appeared around 25.1:

$ for version in 24.3 24.4 24.5 25.1 25.2-rc2 master; do echo "-----
$version -----"; docker run -it -v $(pwd):/rootfs:ro --rm
silex/emacs:$version -Q --batch -l ir-test.el; done
----- 24.3 -----
Interpreted:  Iterative=1.104s; Recursive=0.966s
Bytecompiled: Iterative=0.482s; Recursive=0.633s
----- 24.4 -----
Interpreted:  Iterative=1.096s; Recursive=1.081s
Bytecompiled: Iterative=0.499s; Recursive=0.695s
----- 24.5 -----
Interpreted:  Iterative=1.083s; Recursive=1.087s
Bytecompiled: Iterative=0.497s; Recursive=0.694s
----- 25.1 -----
Interpreted:  Iterative=1.553s; Recursive=1.149s
Bytecompiled: Iterative=0.707s; Recursive=0.590s
----- 25.2-rc2 -----
Interpreted:  Iterative=1.521s; Recursive=1.159s
Bytecompiled: Iterative=0.698s; Recursive=0.602s
----- master -----
Interpreted:  Iterative=1.412s; Recursive=1.357s
Bytecompiled: Iterative=0.439s; Recursive=0.718s