Is hanging a 25kg mirror on 15mm drywall advisable? The mirror has two triangle hanging fixtures either side but they don't align with any studs. I was about to hang 2x brass hooks each with 2x toggle bolts but the two screws each brass hook (http://www.ukpictureframingsupplies.co.uk/ekmps/shops/agfenterprises/images/heavy-duty-wall-hooks-62mm-2-screw-hole-brass-plated-246-p.jpg) would be very close to each other and each hole would be 13mm to fit each toggle bolt through.
I've read that anything over 15kg shouldn't go on drywall only too. Any suggestions?