out of memory

You can either log it or show it on screen directly using following three System.Stats methods:

System.getSystemStats().usedMemory
System.getSystemStats().freeMemory
System.getSystemStats().totalMemory

When you run in the sim, the bottom line of the window tells you memory usage.

Mem: xx.x/yykB peak:zz.zkB

xx.x is what you use when idle, yy is the max allowed on the device you have as a target, and zz.z is the most you've used when running.

With the f5 and 735 and a watchface you have a max of 58kb, while you have 64kb on a 23x or f3, so you might be able to see how close you get. If it runs fine on those and is 59kb peak, that will give you an idea how close you are.

As far as saving memory, it's hard to say without seeing your code. For example, if you are using a bunch of bitmaps all loaded at the same time that could do it, or it could be what variables you use and how you use them, etc. (a single large array could be the issue, or how many colors in a single bitmap)

Oh man, it's that simple ... thank you. The footer of the simulator I have not noticed so far.
I use so far no bitmaps but different fonts. I have to work again and delete unused characters ....

(my code is open source and linked to github :) )

Custom fonts and burn up a lot of space if they are large. And if you are using them to display the time, you can easily cut back to something like 0 to 9 and ":", and not include any letters.