Now study this: https://fxdreema.com/demo/mt4-wrong-closing-rule
many people think that some block should wait for some time and then it will pass and go to the next block. Not true, this does not happen at all. What really happens is that blocks under "on Tick" become active on every tick, again and again, and again, and again - the very same blocks. Well, those on top level at least.
There is no block that will wait 15 candles for something. Blocks work NOW, at the moment. If it's some condition - it works now. If you want to check the current indicator values, fine. If you want to check past indicator values - also fine. Checking future indicator values... no way.
And because so many people think the wrong way, which is in fact the most intuitive way, I thought that I can make it that way... but then I realized that this is not a good idea for some reasons.
So again, you can check anything using the "Condition" block NOW, but the "Condition" block will not wait for the comparison inside to happen. The only block that can wait for some time (but not waiting for something to happen) is called "Delay".
What you can do is to check for crossover NOW and also check for the other indicator 15 candles in the past. Just thing in the opposite way.
Why is that better? Because MetaTrader already have history data that can be accessed. Also because saying that you want to check something in the future requires the use of some variables - the problem here is that if you restart the EA those variables will be gone, they are not persistent. But if you check the past data, in case you restart the EA, that data will still be there and the same, so the EA will continue working as before.