QGIS opening file - very slow on PostGIS database with many layers

When opening a QGIS file with many layers (20 or so) it takes +5 minutes to load. All the layers come from a single PostGIS database.

When looking into the server logs, I see that there are many requests like:

LOG:  SELECT typname,typtype,typelem,typlen FROM pg_type WHERE oid=1700

LOG:  SELECT pg_catalog.format_type(atttypid,atttypmod) FROM pg_attribute WHERE attrelid=34757 AND attnum=3
LOG:  SELECT description FROM pg_description WHERE objoid=34757 AND objsubid=3

Since there are thousands (+3000) of these queries, I suppose the problem lies there...

Any idea?