I imagine that you don't normally teach teachers, so what you'll be showing them will be how you teach learners. I've been on the receiving end of many such talks, and the ones I have found most interesting (therefore the most memorable and the most useful too) have involved practical demonstrations of language-teaching techniques - for which we had to put ourselves in the psoition of language learners. There are two ways to do this, and I've experienced both: you either invent a language (as in the counting exercise I mentioned in another thread); or you do a lesson in a language that none of the teachers present knows. In 15 mins you can't do much, so choose a limited field and use lots of visual aids. Get them handling things and communicating.