MB-100: bumped up loading speed throttle

Change-Id: Ib8504ff0f091ce88d91fa2bd2cd7cb73b1d45124
Reviewed-on: http://review.couchbase.org/26836
Reviewed-by: Ronnie Sun <ronnie@couchbase.com>
Tested-by: Ronnie Sun <ronnie@couchbase.com>