I got lucky with the enemys units and managed to beat stage 14 and did some attemps on 15. A destroyer or artillery at the start is pretty much game over. Once I got lucky and got a good start and managed to push up to the boss but then my heavy died and the enemy summoned 3 destroyers which wrecked my units and then my liutenant.

Then I used my daily reset and started clearing stages again. 14 felt easier than before, cleared it on first attempt. Then I got to 15 again and it had different static defences. Seems the maps switch around a bit when you reset it. That might explain why some other people are also experiencing changes in difficulty.