Very low fps

Hi, i play War thunder since 2 years on a DeL with Core i7, NVIDIA GeForce but since 4 months i have seriously probleme of FPS, i must play in very low quality. At random moment my game turn from 110 FPS to 9 FPS again and again. I try to update my graphique pilot, my computer, delete and install the game and luncher. And now my game is ever under 15 FPS. Idk what to do but i just can’t play. I Hope someone can help me, if you need screen or other i have a discord. Thx

Do you have the problem on another games?
If yes:
Have you cleaned your fan and radiators in your pc?
If your pc is little old, is thermal paste are good?