Signing a document with OpenPGP the <PGPKeyPacket> element in META-INF/documentsignatures.xml contains the full public key, which with many signatures easily can blow up to 1.5MB or more. Optionally only the minimal public key should be included, which is stripped of all signatures except the latest self-signatures.
Gpgme has a GPGME_EXPORT_MODE_MINIMAL flag for this, see https://www.gnupg.org/documentation/manuals/gpgme/Exporting-Keys.html
Thorsten Behrens committed a patch related to this issue.
It has been pushed to "master":
gpg4libre - tdf#113188 add option for minimal PGPKeyPacket
It will be available in 6.0.0.
The patch should be included in the daily builds available at
http://dev-builds.libreoffice.org/daily/ in the next 24-48 hours. More
information about daily builds can be found at:
Affected users are encouraged to test the fix and report feedback.
new hidden config item: Office/Common/Security/OpenPGP/MinimalKeyExport - set to true to get only minimal public key in the key packet
Verified it works as intended.