Convert Real packed array of pairs to Complex packed array

Using Dot is pretty fast:

a = RandomReal[1, {8, 7, 6, 5, 4, 3, 2}];
c = N[{1, I}];

r1 = a.c;// RepeatedTiming

{0.000100, Null}

Get rid of the Apply:

#[[1]] + #[[2]]*I &[
 Transpose[arr, Append[Range[2, Depth[arr] - 1], 1]]]

toCmplx = 
 Compile[{{pair, _Real, 1}}, First@pair + I Last@pair, 
  RuntimeAttributes -> {Listable}]

I believe this works with arbitrary depth, including ragged arrays, so long as the bottom dimension is 2 for all elements. Primitive test with On["Packing"] returned no messages.