1.5.2 is archived because of a weak signature:
Signature algorithm: MD5withRSA (weak), 2048-bit key
But 1.5 had strong signature and thus it remains in the main repo:
Signature algorithm: SHA1withRSA, 2048-bit key
@NicoAlt, looks like algorithm downgrade (SHA-1 -> MD5) happened at some point in the past. Do you know why?