Bump preferred libpq version on MacOS to 15

Fixes #441

Author: jeroen

configure

@@ -19,7 +19,7 @@ PKG_LIBS="-lpq"
 # Extra checks on MacOS for SSL support in libpq
 # command -v is probably fine: https://stackoverflow.com/a/677212/946850
 if [ "`uname`" = Darwin ] && [ "`command -v pkg-config`" ]; then
-  if pkg-config --atleast-version=12 libpq; then
+  if pkg-config --atleast-version=15 libpq; then
     case "`pkg-config --libs --static libpq`" in
     *crypto*)
       echo "Local libpq has SSL support"