Just a guess.
If you have everything at max, you will have a maximum of 20-25 FPS.
My recommendation, setting some graphicssettings (such as Effects other players), to 3 digits. Or hide other players in raids/dungeons completely.
The FPS should be a bit better with that.
Don't forget, B&S is a CPU use game with spaghetti code.
And, i hope you have a decent cooler for your CPU and not this "would like fan" from the CPU box.
This means that the i5 CPU gets too warm very quickly, which the effects that reduces performance (Heat management) which costs performance = less FPS at B&S