The problem is not the amount of data and settings, what makes the watchface slow is the fact, that it uses rotated letters. This means during each draw I must load/unload the font with the desired rotations for each letter and this is slow. But loading all those fonts into memory at once isn’t possible at all because most devices do have 92kB for runtime memory + watchface size in common (even high end devices like the Fenix 6X Pro does only have 128kB).
As long as garmin does not support native support of rotating letters it cannot be improved. If you really can’t accept small delays the few times you start an activity you must switch to a watchface without rotated letters. If garmin ever supports rotating staff on their canvas I will of course improve my watchface.
Every custom watchface does have a higher battery consumption than a default garmin watchface, because every custom watchface must use the SDK whereas garmin can code their watchfaces natively. Regarding battery consumption, I did try to make my watchfaces as good as possible. There are two factors that count when coming to battery consumption - speed of the calculation and screen on time. As written above, speed is not the best in my watchface (altough I’ve optimised it with partial screen updates which are enabled by default) but it’s surely good for the complexity my watchface has. Screen on time depends on you. To minimise both you have following options which should give you really great results in the end: enable the battery saver mode in the watchfaces settings.
If enabled, a simple, super fast and minimal layout will be shown during active battery saver mode times which is as battery friendly as possible. Following options are available:
I want to say, that if you enable always you won’t find another custom watchface that does use less battery as this mode is as simple and fast as possible. Personally, I do use the during sleep option and am content with this.