this problem probaly because of too many background apps
and one more thing .. linux based OS , ram always been used everytime
you can disable some apps like google maps or integrated apps that u dont use
If I helped you, simply click THANKS...
Device : Sony Xperia™ E C1505
ROM : Termin v3.5 by MatsPunt
Kernel : Zeus v3.1.1 by UltraGamerHD
BL : Unlocked + Rooted