They'll be somewhat harder to find after the boosted spawns end. I was in a similar situation myself: https://pokemongo.gamepress.gg/q-a/evolve-ralts-now-or-later
I think it's a bit different in your case since yours is a higher level and the highest level you can power it isn't 40, meaning that it's at a level very close to your max. Also, yours is 15 attack and its lowest stat is its Defense, a stat it doesnt benefit from as much. Its 14 Stamina is good too since it benefits immensely from Stamina. You may want to consider evolving it in your case since you haven't yet found a better alternative. It will evolve to somewhere around 2.6k CP I believe. I also am feeling like they'll switch its moves soon to something slightly worse, although this is just speculation.
Gardevoir is good for taking on Fighting-Types, resisting Blissey's attacks, and for keeping a gym for an EX-Raid (especially when paired with the Normal-type tanks such as Blissey, Slaking, and/or Snorlax).
I say evolve, and you may want to consider it as a Buddy too since you can't do Raids for Ralts Candy.