Yes, check the weight of your empty cases,and consider buying lighter ones. Check the hand baggage limits -size and weight - as it varies between airlines and sometimes between different tour operators on the same flight. You may want to buy extra hand baggage to make the most of that allowance.
For me, the heaviest items are footwear and toiletries, and also a beach towel (which seems to gain weight with accumulated salt and sand!). If you need beach towels, you could consider buying cheap ones there and abandoning them. Take minimal toiletries and see whether you're provided with any in your accommodation; anything else you need can be bought there. Don't agonise over things like tee-shirts, which weigh very little anyway.
Wear your heaviest shoes or sandals, and whatever warmer clothing you're taking. Hand baggage can take your stuff like camera, binoculars, umbrella, guide books and novels (or take a Kindle for your reading matter). You can always pack a spare, empty lightweight shopper or carrier bag and unload your surplus clothing into it once you're through security.
If you're careful, 15kg each plus hand baggage is quite doable, it just needs a bit of thought and a trial pack a couple of days beforehand.