Summoners War: Chronicles

I am newer to the game. In short I played at launch quit and came back the last month or so. My question is their a good way to power up summoner myth equipment to +15 aside from trying to force it using durability stone and prying for the non existent % rng or the succession method? As with both it's going to take me like a year to hit +15 on one piece let alone all summoner equipment. I feel like I'm missing something so any advise/help would be greatly appreciated. 

Right now I am farming Hero raids (usually use 20-30ish additional entries) and Elite raids (use 50-70 additional entries) and am just throwing everything at upgrading the equipment I have and in the last two weeks I have gotten nowhere as in everything is +9 - +13.