I'm wondering at which temperature I should leave my LesP Standard (in the case)

The room I leave it is at : 20 degrees (c)

Should I put it in my room where it is : 22-24 (c)

I'm wondering what is the ideal temperature for storing a guitar?

Humidity is the main issue comparing those two temperatures. Humidity is pretty much always the issue. The only time temperature really matters is when it's extreme or drastic in change. A guitar can sit comfortably from 10-30 degrees. At excessive temperatures, too cold (5 or less) will likely have a dry climate and too hot (+30) will be too wet.

So if your hotter room is at 50% humidity and your cooler room is at 20%, I would keep it in the hotter room. And if the humidity is opposite than I would keep it in the cooler room. Further more is it's 50% humidity in the hot room and 90% in the cool room, I would keep it in the hot room. 40%-60% is recommended.

I use this method :

If you can see your breath infront of you, that room is no good for the guitar.
If you can barely breath in the room for the humidity and heat, that again is no good for the guitar. Other than that, leave it in it's case in whatever room you want for about 10-15mins to adjust to the temp.