Lesley,
1500 kg would seem to be correct for a D5 S60 - but you should check the specification - and see what was actually fitted to your car - because that could increase the actual kerb-weight by 50 kg, 100 kg or more - which is good.
There is no 85% rule - it's a guideline for newbie caravan owners that will hopefully give them a safe towing experience. So follow it as practical advice, but don't let the exact value worry you too much - other than less is better - most drivers can't tell the difference 5% either way would make...
But it's probably a good idea to look at your driving licence and see if it's a B or B+E licence, because that does have implications on what you can tow.
Robert