I'm sure just removing rain particles wouldn't help you much outside from when it's raining. Especially in hardmode, particle effects are all over the place. You'd also run into that problem again, when you're at a snow biome.
Unless your computer is well above the requirements to run Terraria, try messing around with some in-game video options, like frameskipping or try lower your resolution.
If your computer's specs are well over Terraria's system requirements, make sure, that your GPU isn't idling when you're playing.
Terraria lacks a bit of optimization in that regard, with GPU's, who use adaptive power modes, resulting in the game sometimes making the GPU run at 100% clock speeds, then going down to 10% and up to 50% again - back and forth.
To check, if that's the issue, force a constant 50 or 100% clock speed, while playing Terraria. On one of my old GPU's, i work around that, by loading up a random video on my internet browser and pause it, which forces that GPU to stay above 50% clock speeds.
Get a GPU monitoring program, like MSI Afterburner, if you don't already have one installed for confirmation.